৪৯তম বিসিএস ⎯ ফলিত রসায়ন [৫৪১]

প্রশ্ন:


সমাধান:

প্রশ্ন: প্রশ্নবোধক স্থানে কোন সংখ্যাটি বসবে?

সমাধান:
(২য় কলাম × ৩য় কলাম) - ১ম কলাম = ৪র্থ কলাম

(6 × 10) - 2 = 60 - 2 = 58
(7 × 11) - 3 = 77 - 3 = 74
(8 × 12) - 4 = 96 - 4 = 92

সুতরাং, প্রশ্নবোধক স্থানে 92 সংখ্যাটি বসবে।

Fermentation:
Energy is supplied chemically from the substrate (e.g., glucose) via biochemical metabolism by microorganisms.
No external electrical energy is applied.
Electrolysis:
Energy is supplied externally in the form of electricity to drive non-spontaneous chemical reactions.

Other options:
ক) Heat transfer is not the main distinguishing factor.
খ) Reaction medium may vary in both processes (aqueous solutions, etc.).
গ) Pressure conditions are not universally different between the two.

1.Photochemical processes are chemical reactions initiated or accelerated by light (usually UV or visible light).
2.Photosensitized polymerization:
Uses light-sensitive catalysts to initiate polymerization of monomers.
Common in industrial production of certain plastics and resins.

Other options:
খ) Electrolysis is an electrochemical process, driven by electricity.
গ) Thermal cracking is a thermal process, driven by heat.
ঘ) Calcination is a thermal process, also driven by heat, not light.

Process intensification (PI) in chemical engineering aims to make chemical processes more efficient, safer, and compact by:
1.Integrating multiple unit operations into a single step.
2.Enhancing mass and heat transfer.
3.Reducing energy consumption and equipment footprint.
Examples:
1.Reactive distillation (reaction + separation in one unit)
2.Microreactors for fast and controlled reactions
3.Combined extraction and reaction units

Other options:
ক) Increasing plant size is not PI, it’s conventional scale-up.
গ) Using hazardous chemicals is unsafe and not PI.
ঘ) Increasing residence time may improve conversion but is not the essence of PI.

1.Biochemical technology involves processes where biological agents (microorganisms, enzymes) are used to carry out chemical transformations.
2.Alcohol fermentation:
Uses yeast or bacteria to convert sugars into ethanol and CO₂.
Classic example of a biochemical process in industrial technology.

Other options:
ক) Electro-winning of copper → Electrochemical process.
খ) Polymerization → Chemical (synthetic) process.
ঘ) Chlorination → Chemical process involving chlorine, not biological agents.

1.Green chemistry aims to design chemical products and processes that:
Reduce or eliminate hazardous substances.
Conserve resources and energy.
Minimize environmental impact and waste.
2.It is considered a major development because it integrates sustainability into chemical technology, promoting safer, cleaner, and more efficient industrial practices.

Other options:
ক) Green chemistry is not just about cost reduction.
খ) Heat can still be used; the focus is on safety and sustainability, not eliminating heat.
গ)Catalysts are often encouraged in green chemistry to increase efficiency and reduce waste.

Preliminary feasibility analysis is the first and crucial step in chemical project design:
1. Evaluates technical, economic, and market viability.
2.Identifies potential challenges, risks, and resource requirements.
3.Forms the basis for deciding whether to proceed with detailed design and investment.

Other options:
ক) Plant layout comes later, after feasibility and process design.
গ) Equipment procurement occurs during detailed engineering, not initially.
ঘ) Environmental clearance is applied for after preliminary project planning.

1.Fixed Capital Investment (FCI) refers to the capital spent on physical, long-term assets required to set up a chemical plant.
2.It typically includes:
Land and site development
Buildings and structures
Machinery and equipment
Installation and commissioning costs

Other options:
ক) Raw material costs → Part of working capital, not FCI.
খ) Salaries and wages → Operating expenses, not fixed capital.
ঘ) Utility bills → Recurring operating costs, not FCI.

1.Contingency allowance is an additional amount added to the estimated project cost to account for:
Unexpected expenses during construction or commissioning
Design changes
Market fluctuations in material or labor costs
Other uncertainties
2.It ensures that the project remains financially viable even if unforeseen costs arise.

Other options:
ক) Cover inflation only → Inflation is usually accounted for separately, not solely by contingency.
খ) Increase IRR → Contingency doesn’t affect IRR; it’s a risk management tool.
গ) Reduce tax liability → Contingency has no direct effect on taxes.

Detailed Engineering Design (DED) is the stage where the technical design of the plant is finalized:
1.Development of Process Flow Diagrams (PFDs).
2.Preparation of Piping & Instrumentation Diagrams (P&IDs).
3.Selection of equipment specifications, materials, and control systems.
4.Basis for procurement, construction, and commissioning.

Other options:
ক) Market survey and demand forecasting → Part of preliminary feasibility and project planning.
গ) Financial appraisal → Conducted during project feasibility study, not DED.
ঘ) Project closure report → Prepared at the end of the project, after commissioning.

Project commissioning is the stage where the installed plant or equipment is tested and brought into operation:
Ensures all systems, instruments, and equipment function as designed.
Involves trial runs, process adjustments, and safety checks.
Marks the transition from construction to full production.

Other options:
ক) Initial conceptualization → Part of project planning/feasibility study.
খ) Final approval by financial institutions → Part of project financing, not commissioning.
ঘ) Employee recruitment → HR activity, not the core purpose of commissioning.

1.In Bangladesh, any chemical or industrial project must obtain an Environmental Clearance Certificate (ECC) from the Department of Environment (DOE) before construction or operation.
2.The ECC ensures that the project:
Complies with environmental regulations.
Minimizes air, water, and soil pollution.
Implements waste management and safety measures.

Other options:
ক) Local union membership is not a legal pre-condition.
খ) Government subsidies are optional and not legally required.
ঘ) NGO approval is advisory, not a legal requirement.

Many chemical industries in Bangladesh face frequent power interruptions and insufficient energy supply, which:
Disrupt continuous processes.
Reduce productivity and efficiency.
Increase operational costs due to backup power requirements.

Other options:
ক) Excessive domestic demand → Demand is generally growing but not a problem; the issue is supply constraints.
গ) Overabundance of skilled engineers → Actually, there is often a shortage of experienced chemical engineers.
ঘ) Too many R&D facilities → R&D facilities are limited, not excessive.

Many chemical industries in Bangladesh face environmental compliance issues because:
1.Effluents often contain toxic chemicals, heavy metals, and high BOD/COD.
2.Advanced ETPs are either absent or inadequate, leading to non-compliance with DOE regulations.
3.Results in pollution of rivers, soil, and groundwater.

Other options:
ক) Enforcement exists but zero-discharge policies are not fully applied; lack of treatment is the bigger problem.
খ) Green chemistry practices are rarely implemented, not excessive.
গ) Over-investment in waste minimization is not the issue; under-investment is.

Bangladesh tanneries, especially in areas like Hazaribagh, generate large amounts of chromium-laden and toxic wastewater.
CETPs (Common Effluent Treatment Plants):
1.Centralized facilities where multiple tanneries discharge their effluents.
2.Treat wastewater to meet environmental standards before discharge into rivers.
3.More cost-effective and manageable than individual treatment plants for each tannery.

Other options:
ক) Shifting to residential areas would increase public exposure and is unsafe.
গ) Simply increasing temperature does not remove chromium; proper chemical treatment is required.
ঘ) Burning waste without emission control is highly polluting.

1.Chemical plants require a continuous and reliable energy supply for heating, cooling, running reactors, pumps, and compressors.
2.In Bangladesh, plants often face:
Frequent load-shedding
Gas supply shortages
Unstable electricity
3.These issues lead to:
Production interruptions
Increased costs due to backup generators or fuel
Safety risks in sensitive chemical processes

Other options:
খ) Raw material storage is generally manageable; oversupply is not a main problem.
গ) There is usually a shortage, not excess, of skilled operators.
ঘ) Domestic demand is growing; lack of market is not the main challenge.

1.Compressibility refers to the variation of fluid density with pressure.
2.For gases:
At low speeds (Mach < 0.3), density changes are small → flow can often be treated as incompressible.
At higher speeds (Mach > 0.3), density changes become significant → compressibility effects must be considered.
3.For liquids:
They are mostly incompressible under normal conditions, but compressibility can matter at very high pressures.

Other options:
খ) Not always negligible; under very high pressures, liquid compressibility matters.
গ) Compressibility depends on pressure, temperature, and flow velocity, so it is not independent of velocity.
ঘ) Compressibility affects both density and pressure in gases; it is not limited to density only.

1.Viscosity is a measure of a fluid’s resistance to shear deformation.
2.Fluids cannot sustain shear stress under static conditions; they flow when a shear stress is applied.
3.The rate of flow under a given shear stress is directly related to the fluid’s viscosity:
High viscosity → flows slowly (e.g., honey)
Low viscosity → flows easily (e.g., water)

Other options:
ক) Bulk modulus → Measures resistance to compression, not shear.
খ) Surface tension → Relevant to interfaces, not shear transmission in bulk fluid.
গ) Density → Affects inertia and weight, not shear response.

1.Euler’s equation describes the motion of an ideal (inviscid) fluid.
2.It is derived by applying Newton’s second law (F = ma) to a differential fluid element, considering:
Pressure forces
Body forces (e.g., gravity)
Acceleration of the fluid element
3.Euler’s equation is the foundation for inviscid flow analysis and is a generalization of Newton’s laws to a continuous fluid.

Other options:
ক) Euler’s equation includes inertia (acceleration) terms, not just pressure and gravity.
গ) Conservation of angular momentum is related to rotational dynamics, not the primary basis of Euler’s equation.
ঘ) Bernoulli’s equation can be derived from Euler’s equation for steady, incompressible, inviscid flow along a streamline, but Euler’s equation is more general.

Orifice plate flow meters operate based on differential pressure measurement:
1. A restriction (orifice) is placed in the pipeline.
2. Fluid velocity increases through the orifice, causing a pressure drop across it.
3.The flow rate is calculated from this pressure difference using Bernoulli’s principle.

Other options:
খ) Rotameter → Measures flow based on float position in a tapered tube (variable area).
গ) Magnetic flow meter → Measures flow using Faraday’s law of electromagnetic induction, not pressure drop.
ঘ) Ultrasonic flow meter → Measures flow by transit time or Doppler shift of ultrasonic waves, not differential pressure.

Hydrostatic pressure in a fluid at rest is given by:
P=P0+ρgh
where:
P0 = pressure at the free surface (often atmospheric)
ρ = fluid density
g= acceleration due to gravity
h = depth below the free surface

Other options:
ক) Shape of container does not affect hydrostatic pressure.
খ) Orientation is irrelevant; pressure at a depth is the same in all directions.
ঘ) Cross-sectional area does not influence pressure at a given depth.

Mixed-potential theory states that the overall corrosion potential (E_corr) of a metal in an electrolyte is established when:
1.Anodic reaction (metal dissolution) and
2.Cathodic reaction (usually oxygen reduction or hydrogen evolution)
3.Occur simultaneously with equal current densities.
On a polarization curve plot:
1.Anodic curve: current vs. potential for metal oxidation
2.Cathodic curve: current vs. potential for reduction reaction
3.Intersection point: Determines the corrosion potential (E_corr) and corrosion current density (i_corr).

Other options:
খ) Maximum anodic current does not define corrosion potential.
গ) Open-circuit potential of the cathode alone is insufficient.
ঘ) Standard reduction potential of the anode is reference, but real corrosion potential depends on both anodic and cathodic reactions.

1.Corrosion of carbon steel in acidic solutions is generally controlled by electrochemical kinetics.
2.Increasing temperature:
Accelerates both anodic (metal dissolution) and cathodic (hydrogen evolution) reactions.
ncreases the corrosion rate exponentially due to Arrhenius-type temperature dependence.

Other options:
ক) Increase in solution resistivity → Higher resistivity reduces ionic conductivity, slowing corrosion.
খ) Increase in oxygen overpotential → In acidic solution, hydrogen evolution dominates, so oxygen effect is minimal.
গ) Decrease in hydrogen ion concentration → Lower [H⁺] reduces the corrosion rate because acidic attack is slower.

Cathodic protection (CP) works by supplying a direct current (DC) to the metal structure to make it the cathode of an electrochemical cell.
DC current ensures:
1. Continuous electron flow to the metal.
2.Suppression of the anodic reaction (metal dissolution).
Why not AC:
1.AC current alternates direction, so the metal alternately becomes anode and cathode.
2.This cancels out net protection and may even accelerate corrosion.

Other options:
ক) AC does not inherently cause passivation.
খ) AC itself does not specifically accelerate galvanic corrosion.
ঘ) Hydrogen embrittlement is more associated with high DC cathodic overprotection, not AC.

1.Intergranular corrosion occurs along grain boundaries due to chromium carbide precipitation (sensitization) in stainless steels when exposed to 450–850 °C (such as during welding).
2.This depletes chromium at grain boundaries, making them anodic and susceptible to attack, especially in aggressive environments like chemical plants.

Other options:
ক) Boiler tubes in high-pressure steam service → more prone to stress corrosion cracking, caustic embrittlement, or oxidation.
গ) Zinc coatings in atmospheric exposure → usually face uniform corrosion, pitting, or white rust, not IGC.
ঘ) Copper pipelines in potable water systems → mainly suffer from pitting corrosion, erosion–corrosion, or dezincification (if brass), not IGC.

ক) Activation-controlled region:
The linear region of a Tafel extrapolation curve corresponds to the activation-controlled region, where the corrosion rate is governed by the kinetics of the electrochemical reactions (charge transfer). In this region, the relationship between the logarithm of the current density and the overpotential is linear, allowing for the determination of the corrosion rate using Tafel extrapolation.

Other Options:
খ) Diffusion-controlled region: This occurs when mass transport limits the reaction, typically at higher overpotentials, where the curve deviates from linearity.
গ) Mixed-control region: This involves both activation and diffusion control, resulting in a non-linear region on the Tafel plot.
ঘ) Passive region: This corresponds to a region where a protective oxide layer forms, reducing corrosion rate, and is not part of the linear Tafel region.

1.Tafel extrapolation relies on the assumption that corrosion kinetics are controlled by charge-transfer (activation polarization) at the electrode surface.
2.In this region, the current–potential relationship is logarithmic (straight line on semi-log plot).

Other options:
Diffusion-controlled region (খ) shows a limiting current plateau, not a linear Tafel slope.
Mixed-control region (গ) does not give a clean straight line, making extrapolation unreliable.
Passive region (ঘ) shows current suppression due to passive film, not Tafel behavior.

In the upper zone (below ~700 °C), hydrogen (H₂) and CO both contribute, but H₂ is more effective at lower temperatures.
At higher temperatures (>700 °C), CO is the dominant reducing agent because:
1.CO concentration is high (from the Boudouard reaction: C + CO₂ ⇌ 2CO).
2.Direct reduction with solid carbon (option খ) is too slow in practical furnace operation.

1.Wrought iron contains very little carbon (<0.08%) but a significant amount of slag (iron silicate, Fe₂SiO₄) inclusions, elongated during rolling/forging.
2.These fibrous slag inclusions improve toughness, ductility, and resistance to crack propagation, allowing forging at relatively low temperatures.

other options:
ক) Low silicon content → true for wrought iron, but not the main reason for forgeability.
খ) High carbon content → incorrect, wrought iron is low-carbon, unlike steel/pearlite structures.
ঘ) High sulfur content → harmful, makes iron brittle (“hot shortness”), not forgeable.

1.For hypoeutectoid steels (<0.8% C): Proeutectoid ferrite forms along austenite grain boundaries before pearlite.
2.For hypereutectoid steels (>0.8% C): Proeutectoid cementite forms along austenite grain boundaries before pearlite forms inside the grains.
3.At the eutectoid temperature (A₁ ≈ 727 °C), the remaining austenite transforms to pearlite.

1.Chromium (Cr) is a strong carbide former and refines the microstructure.
2.It increases hardenability by slowing down the transformation of austenite to pearlite, allowing deeper hardening during quenching.
3.It also provides corrosion resistance by forming a thin, stable, adherent Cr₂O₃ passive film on the surface (basis of stainless steels with >12% Cr).

Other options:
খ) Chromium does not significantly lower the melting point of steel.
গ) Chromium slows pearlite formation but does not prevent it entirely.
ঘ) Electrical conductivity is actually reduced, not increased, by alloying elements.

Determine the minimum number of stages at total reflux: The Fenske equation calculates the minimum theoretical stages needed for a distillation separation at total reflux, assuming constant relative volatility.

Other options:

ক) Minimum reflux ratio: Calculated using Underwood equations or McCabe-Thiele, not Fenske.
গ) Murphree tray efficiency: Measures real tray performance, unrelated to Fenske.
ঘ) Pressure drop across a tray: Determined by tray hydraulics, not Fenske.

Flooding = excessive vapor flow pushes liquid upward, preventing proper downflow through downcomers → trays cannot function properly, pressure drop increases, and efficiency drops sharply.

other options:
ক) Vapor velocity too low → leads to weeping (liquid leaks through perforations instead of flowing across tray).
খ) Reflux ratio below minimum → column cannot achieve desired separation, but it doesn’t cause flooding.
গ) Feed at bubble point → this is the definition of a saturated liquid feed (q = 1), not flooding.

1.The feed condition (subcooled liquid, saturated liquid, mixture, or superheated vapor) is represented by the q-line.
2.The rectifying operating line (above the feed) and the stripping operating line (below the feed) must both pass through the feed point, which is where they intersect the q-line.
3.This intersection defines the feed stage location.

Other options:
ক) Equilibrium curve → relates liquid–vapor equilibrium, not feed stage.
খ) Operating lines intersect equilibrium curve → used for stage stepping, not feed stage location.
ঘ) Minimum reflux ratio → determined by the pinch point, not feed location.

1.Sieve trays are just perforated plates — simple, cheap, and easy to fabricate compared to bubble-cap trays (which require risers and caps, making them costly and complex).
2.They also offer higher capacity (can handle higher vapor and liquid loads) with lower pressure drop, making them suitable for large columns.

Other options:
ক) Higher efficiency at low vapor rates → actually bubble-cap trays perform better at very low vapor rates; sieve trays may weep.
গ) Minimize column height → column height depends on separation duty (number of stages), not tray type.
ঘ) Prevent entrainment better → bubble-cap trays resist weeping and entrainment better than sieve trays.

To recap succinctly:
Sieve trays: simple perforated plates → cheap, easy to fabricate, higher capacity, suitable for large-scale columns.
Bubble-cap trays: more complex (caps + risers) → better at low vapor rates and preventing weeping/entrainment, but costly and lower capacity.

So, for large industrial columns, fabrication simplicity and higher throughput make sieve trays the preferred choice.

1.A compression–absorption cascade system combines a vapor-compression cycle with an absorption cycle:
1.The compression stage handles moderate-temperature lifts efficiently.
2.The absorption stage allows the low-temperature side to reach very low evaporator temperatures with less mechanical work, using thermal energy instead.
2.This setup is ideal for ultra-low temperature applications (e.g., cryogenics) where purely mechanical compression would be inefficient or require very high compression ratios.

Other options:
ক) Partial advantage, but the key benefit is low-temperature capability with reduced compressor work.
খ) Solution heat exchangers are still used to improve efficiency.
গ) Increasing condenser pressure is not the primary thermodynamic advantage.

1.The solution heat exchanger preheats the strong (rich) ammonia solution entering the generator using the hot weak (lean) solution leaving the generator.
2.This reduces the external heat input required in the generator, improving the cycle’s coefficient of performance (COP).

Other options:
খ) Generator temperature just above ammonia’s boiling point → low generator temperature may limit ammonia vapor production and reduce COP.
গ) Evaporator temperature = condenser temperature → no refrigeration effect occurs; COP would be zero.
ঘ) High absorber pressure → may affect ammonia absorption, but excessive pressure can reduce driving force and hurt COP.

1.Higher ammonia concentration in the strong solution means more refrigerant (NH₃) is available for evaporation in the evaporator → higher refrigerating effect.
2.However, the generator must supply more heat to boil off the extra ammonia, which may require higher generator temperatures.

Other options:
খ) Absorber performance may actually improve because more ammonia can be absorbed, not reduce due to solubility.
গ) COP doesn’t necessarily decrease; it can improve if the heat input is efficiently managed.
ঘ) The effect is significant, not negligible.

1.The evaporator temperature is directly related to the vapor pressure of ammonia: lower evaporator temperatures require lower ammonia partial pressures.
2.In a water–ammonia system, water acts as the absorbent, so the ammonia vapor pressure in the evaporator is limited by the solution composition and absorber operation.

Other options:
ক) Generator temperature → affects the driving force for ammonia desorption, not directly the lowest evaporator temperature.
খ) Absorber temperature → affects absorption efficiency but not directly the minimum evaporator temperature.
ঘ) Condenser pressure → sets the high-pressure side; it does not limit how low the evaporator can go.

1.Subcooling lowers the temperature of the liquid refrigerant below its condensation temperature, increasing its enthalpy difference across the expansion valve.
2.This means:
More cooling effect per kg of refrigerant → lower mass flow rate required for the same cooling load.
Improved cycle efficiency (higher COP) because less work is needed per unit cooling.

Other options:
খ) Pressure drop across the expansion valve is largely unaffected by subcooling.
গ) COP does improve, not neutral.
ঘ) Subcooling does not reduce condenser temperature; it only reduces refrigerant temperature after condensation.

1.Tropospheric (ground-level) ozone is not emitted directly; it is a secondary pollutant.
2.It forms via photochemical reactions:
1.NO₂ + sunlight → NO + O
2.O + O₂ → O₃
3.VOCs react with NO to regenerate NO₂, sustaining ozone formation.

Other options:
খ) O₃ is rarely emitted directly; it forms in the atmosphere.
গ) CO₂ and methane contribute to greenhouse effect, not directly to ozone formation.
ঘ) SO₂ reacts with water to form sulfuric acid, not ozone.

1.Anaerobic treatment generates sulfide ions (S²⁻) from the reduction of sulfate by sulfate-reducing bacteria.
2.Metal sulfides precipitate according to their solubility products (Ksp).
3.Lead sulfide (PbS) has an extremely low Ksp (~10⁻²⁸) → precipitates readily.

Other options:
Chromium (Cr³⁺) → Cr₂S₃ is less insoluble, slower precipitation.
Mercury (Hg²⁺) → HgS is also insoluble, but Hg²⁺ is less commonly present in large quantities in typical industrial wastewater.
Copper (Cu²⁺) → CuS has a higher solubility than PbS; precipitation is less complete.

As we know that,
Radiative forcing , ΔF= 5.35 ln(C/​C​₀) W/m²
= 5.35 ln (420/280)
= 2.17 W/m²
≈ 2.0 W/m²

1.Polar ozone depletion is largely caused by chlorine radicals (Cl·) released from chlorofluorocarbons (CFCs) on polar stratospheric clouds (PSCs).
2.During Antarctic spring, sunlight photolyzes Cl₂ and other chlorine reservoirs, producing active Cl radicals:
Cl+O₃→ClO+O₂
CIO participates in catalytic cycles that destroy ozone repeatedly.

Other options:
খ) O₂ + O → O₃ → ozone formation, not depletion.
গ) CO₂ + UV → CO + O → not relevant to stratospheric ozone.
ঘ) NO + O₃ → NO₂ + O₂ → part of NOₓ cycle, minor in polar depletion compared to Cl.

Given:

Wastewater flow Q=500 m³/day
COD = 2,500 mg/L = 2,500 g/m³ (since 1 mg/L = 1 g/m³)
COD removal efficiency = 85%

COD load=Q×COD concentration=500 m³/day×2,500 g/m³=1,250,000 g/day

Convert to kg/day:
1,250,000 g/day=1,250 kg/day

COD removed=85%×1,250 kg/day=0.85×1,250=1,062.5 kg/day

1.Jar testing is used to determine the optimum coagulant dose, such as alum, for water treatment.
2.At the optimum dose, colloidal particles are effectively neutralized, aggregate into flocs, and settle out, resulting in reduced turbidity.
3.Overdosing alum can lead to charge reversal or excess positive charge on particles. This causes the particles to repel each other, breaking up flocs or preventing their formation.
4.As a result, turbidity can increase instead of decreasing, a phenomenon known as restabilization of colloids.

Other options:
ক) is true only at optimum dosing, not overdosing.
গ) complete neutralization occurs at optimum, not beyond.
ঘ) excessive chlorine demand is unrelated to alum dosing.

1.In electrodialysis (ED), ions move through selective membranes under an electric field to desalinate water.
2.Limiting current density (LCD) is the maximum current density at which ions can be transported from the bulk solution to the membrane surface without causing problems.
3,If the applied current exceeds the LCD:
1.Concentration polarization occurs: ion concentration at the membrane surface drops to near zero.
2.Water splitting happens at the membrane (H⁺ and OH⁻ generation), which can damage membranes and reduce ion removal efficiency.
3.Energy consumption increases without additional desalination benefit.

Other options:
ক) Freezing is not related to current density.
গ) pH may change locally due to water splitting but is not the primary effect.
ঘ) Microbial growth is influenced by biofouling, not LCD.

1.Ultrafiltration (UF) membranes have very small pores (~0.01–0.1 μm) and are excellent for removing colloids, pathogens, and fine particles.
2.However, large suspended solids and turbidity in surface water can rapidly foul or clog the UF membrane, reducing flow (flux) and increasing operational problems.
3.Therefore, pre-treatment by coarse filtration or sedimentation is done to remove large particles before UF, which:
Protects the membrane
Maintains higher flux rates
Reduces cleaning frequency and chemical usage

Other options:
খ) Dissolved salts pass through UF; they are not removed by pre-filtration.
গ) pH neutralization is a separate chemical treatment, not done by sedimentation.
ঘ) Coarse filtration does not replace coagulation; coagulation may still be needed for colloids.

1.In an activated carbon (AC) filter, adsorption gradually removes contaminants from water.
2.Breakthrough occurs when the adsorbent becomes partially saturated, and contaminants begin appearing in the effluent.
3.It is usually defined as the point where the effluent concentration reaches a small fraction (commonly 5–10%) of the influent concentration.
4.After breakthrough, the filter can no longer guarantee effective removal, and regeneration or replacement of carbon is needed.

Other options:
ক)100% removal never occurs; breakthrough happens much earlier.
খ) Carbon particles do not dissolve into water; AC is insoluble.
ঘ) Chlorine disappearance is unrelated to AC adsorption.

Given:
Influent BOD = 180 mg/L
BOD removal = 85%

BOD removed=180×85/100​=180×0.85=153 mg/L
BOD remaining=180−153=27 mg/L

1.The Frasch process is used to extract elemental sulfur from underground deposits.
2.Superheated water (around 165–180 °C) under pressure is injected to melt the sulfur, which has a melting point of about 115 °C.
3.Compressed air or hot water is then used to push the molten sulfur to the surface through pipes.
4.The sulfur remains elemental, not dissolved chemically or reacted.

Other options:
ক) Sulfur is not soluble enough in water to be pumped in solution.
গ) No reaction with hydrogen occurs; H₂S is not formed.
ঘ) Sulfur is not converted to sulfuric acid in situ.

1.In the contact process, SO₂ is oxidized to SO₃ over a V₂O₅ catalyst.
2.The reaction is:
2SO₂+O₂→V₂O₅2SO₃
3.This reaction is exothermic and temperature-dependent.
4.Lower-than-optimal temperatures reduce the reaction rate, leading to incomplete conversion of SO₂ to SO₃, which means more SO₂ is released in the off-gas, causing excess emissions.

Other options:
খ) High-pressure air in the absorption tower affects absorption efficiency, not SO₂ formation.
গ) Adding water to SO₃ directly causes sulfuric acid mist and is dangerous, but does not increase SO₂ emissions.
ঘ) Rapid cooling may cause SO₃ condensation issues but is not the primary cause of excess SO₂.

1.Acid rain is primarily caused by SO₂ and NOₓ emissions, which react with water in the atmosphere to form acids.
2.H₂S in natural gas is a major sulfur source. Burning it directly would produce SO₂.
3.The Claus process converts H₂S into elemental sulfur before combustion:
2H₂S+O₂→2S+2H₂O
4.This prevents SO₂ formation, thereby mitigating acid rain.

Other options:
ক) Using high-sulfur coal increases SO₂ emissions → worse acid rain.
খ) Roasting sulfide ores in open pits releases SO₂ → contributes to acid rain.
গ) Venting SO₂ directly releases pollutants → worsens acid rain.

Roasting pyrite (FeS₂) produces sulfur dioxide (SO₂):
4FeS₂+11O₂→2Fe₂O₃+8SO₂
If SO₂ is not captured or converted to sulfuric acid, it can react with water in the atmosphere to form acid rain, which harms soil, water bodies, vegetation, and buildings.

Other options:
ক) Not all environmental emissions are neutralized; uncontrolled SO₂ is harmful.
খ) Roasting consumes oxygen but generates pollutants (SO₂).
ঘ) Elemental sulfur is not the main product of pyrite roasting; SO₂ is.

1.Industrial sulfur recovery, such as the Claus process, is designed in thermal and catalytic stages:
Thermal stage: H₂S is partially combusted to form SO₂ and elemental sulfur at high temperatures.
Catalytic stage(s): Remaining H₂S reacts with SO₂ over a catalyst (typically Al₂O₃ or TiO₂) to produce more elemental sulfur:
2H₂S+SO₂→3S+2H₂O
2.Using both stages ensures:
1.High conversion efficiency of H₂S to elemental sulfur (often >95%)
2.Minimal SO₂ emissions, reducing environmental pollution

Other options:
ক) Melting point is irrelevant; sulfur is produced as a solid or molten form as needed.
গ) Sulfur is not directly converted to H₂SO₄ in this process; separate acid plants handle that.
ঘ) SO₂ is not intentionally produced for power generation here; it’s a by-product to be minimized.

1.In industrial urea production, ammonia (NH₃) and carbon dioxide (CO₂) react to form ammonium carbamate:
2NH₃+CO₂⇌NH₂COONH₄
2.​The carbamate is then dehydrated to urea:
NH₂COONH₄→(NH₂₎₂CO+H₂O
3.The stripping column serves to:
Remove unreacted NH₃ and CO₂ from the solution
Recycle them back to the reactor for efficiency
4.This ensures maximum urea yield and reduces losses of reactants.

Other options:
খ) Water evaporation is done in concentrators/evaporators, not the stripping column.
গ) Urea is not converted to ammonium nitrate in this step.
ঘ) Cooling before granulation is done in the prilling or granulation section, not in the stripping column.

1.TSP (Triple Superphosphate, Ca(H₂PO₄)₂·H₂O) is produced by reacting phosphate rock with concentrated phosphoric acid:
Ca₃(PO₄)₂+4H₃PO₄→3Ca(H₂PO₄)₂
​2.High P₂O₅ content in TSP depends on:
1.Finely ground phosphate rock → increases surface area, improving reaction with acid.
2.Proper acid concentration → ensures complete conversion of phosphate rock to soluble mono-calcium phosphate.
3.Other factors like water addition, sintering, or ammonia are either irrelevant or not used in standard TSP production.

Other options:
ক) Excess water dilutes acid, reducing P₂O₅ content.
খ) TSP is not sintered; sintering applies to DAP production.
গ) Ammonia is used in DAP/MAP, not TSP.

1.In urea plants, unreacted ammonia from the reactor and stripper can escape as vapor, contributing to air pollution and odor problems.
2.Scrubbing involves passing these gases through a dilute acid solution (commonly sulfuric or phosphoric acid), which reacts with NH₃ to form ammonium salts:
NH₃+H₂SO₄→(NH₄)₂SO₄
​3.This prevents direct release of ammonia, reduces environmental impact, and can even produce a useful by-product.

Other options:
ক) Direct release would increase NH₃ pollution.
গ) Increasing pressure beyond optimal limits is inefficient and unsafe.
ঘ) Cooling urea melt does not remove gaseous NH₃ effectively.

1.Ammonia (NH₃) synthesis requires hydrogen (H₂) and nitrogen (N₂).
2.In Bangladesh, the main source of hydrogen is natural gas, which is abundant. The process is:
Steam reforming of natural gas (mostly CH₄):
CH₄+H₂O→CO+3H₂
Shift reaction to convert CO to CO₂:
CO+H₂O→CO₂+H₂
3.Hydrogen is then purified and fed, along with nitrogen, into the Haber–Bosch process to produce ammonia.

Other options:
খ) Direct electrolysis is too energy-intensive for industrial-scale H₂ production.
গ) Roasting phosphate rock produces P₂O₅, not hydrogen.
ঘ) Decomposition of ammonium nitrate is unsafe and produces N₂, O₂, and heat, not a reliable H₂ source.

1.TSP (Triple Superphosphate) is produced by reacting phosphate rock with concentrated phosphoric acid:
Ca₃(PO₄)₂+4H₃PO₄→3Ca(H₂PO₄)₂
2.Phosphate rock often contains fluorides (F⁻) and other impurities. During acid treatment:
Fluoride compounds can be released into wastewater or air.
Acidic effluents are generated, which can harm soil and water bodies if not treated.

Other options:
ক) Carbon dioxide emissions are mainly associated with urea, not TSP.
খ) Nitrogen oxides are relevant to ammonia synthesis, not TSP.
গ) Elemental sulfur is not a by-product of TSP production.

1.In sugarcane processing, the raw juice contains sugars along with non-sugar impurities like proteins, organic acids, and suspended solids.
2.Defecation is the process of:
Adding lime (Ca(OH)₂) to the juice
Heating the juice to precipitate impurities
3.The precipitated solids (mud) are then removed, leaving a clearer juice suitable for evaporation and crystallization.

Other options:
খ) Crystallization occurs later in the sugar boiling step, not defecation.
গ) Fermentation of molasses is for ethanol production, unrelated to defecation.
ঘ) Drying bagasse is for fuel use, not impurity removal.

1.Press mud (also called filter cake) is the solid residue left after clarifying sugarcane juice during the defecation process.
2.It is rich in:
Organic matter
Potassium, phosphorus, and other nutrients
3.Therefore, it is commonly used as a soil conditioner or organic fertilizer to improve soil fertility.

Other options:
ক) Bagasse, not press mud, is typically used as boiler fuel.
খ) Press mud is not generally used for ethanol fermentation.
ঘ) Press mud does not contain significant recoverable sugar for direct extraction.

1.In Bangladesh, sugar mills face operational inefficiencies primarily due to:
Irregular or insufficient supply of sugarcane → reduces mill throughput and affects continuous operation.
Outdated machinery and technology → lowers extraction efficiency and sugar recovery.
2.These factors together limit overall sugar production and quality.

Other options:
ক) High technological standard would increase efficiency, not limit it.
গ) Sugar beet cultivation is minimal in Bangladesh; it does not affect sugarcane-based mills.
ঘ) Bagasse is used as fuel, but overuse is generally not a limiting factor; it mainly provides energy.

1.Most coal deposits in Bangladesh, including Barapukuria and Phulbari, are thermally mature coals of the bituminous to sub-bituminous rank.
2.Characteristics:
Moderate carbon content (higher than lignite, lower than anthracite)
Reasonable calorific value suitable for power generation

Other options::
ক) Anthracite: Rare or absent in Bangladesh; very high carbon and energy content.
খ) Lignite: Low-rank coal, mostly brown coal, less abundant in these regions.
গ) Peat: Pre-coal stage, very low carbon content, not significant in Barapukuria or Phulbari.

1.Coal carbonization (coking) involves heating coal in the absence of air to produce coke.
2.The main byproducts include:
Coal tar – a viscous liquid containing aromatic compounds; widely used in chemical industries for dyes, chemicals, and pharmaceuticals.
Ammonia, benzene, and other volatile compounds – also recoverable.

Other options:
ঘ) Char – solid residue (coke), used mainly as fuel, not a chemical feedstock.
খ) Fly ash – comes from coal combustion, not carbonization.
গ) Sulfur dioxide – formed during combustion, not a recoverable product in carbonization.

1.Syngas (synthesis gas) is produced from coal gasification, where coal reacts with steam and a controlled amount of oxygen at high temperatures:
C+H₂O→CO+H₂
2.​Typical composition of syngas:
Carbon monoxide (CO)
Hydrogen (H₂)
Minor amounts of CO₂, CH₄, and other trace gases
3.Syngas is a key intermediate for ammonia, methanol, and synthetic fuels.

Other options:
ক) Methane and ethane are present only in small quantities.
গ) CO₂ and N₂ are byproducts or diluents, not the main syngas components.
ঘ) Oxygen and ozone are not part of syngas; oxygen is only a reactant.

Coal mining in Bangladesh, especially in Barapukuria and Phulbari, is mainly underground or open-pit mining.
Key environmental challenges include:
1.Land subsidence → collapsing of land after coal removal
2.Lowering of water table → affecting local wells and agriculture
3.Disposal of overburden and mine waste

Other options:
খ) Excessive anthracite production is not relevant; Bangladeshi coal is mostly sub-bituminous/bituminous.
গ) Sulfur content cannot be completely eliminated in mining; it’s a chemical property, not a mining challenge.
ঘ) Spontaneous combustion is rare for low-rank coals found in Bangladesh.

1.Bangladesh has very limited indigenous crude oil reserves, making the country heavily dependent on imported crude for its refineries.
2.This restricts the scale and reliability of domestic petroleum refining capacity.

Other options:
খ) There is no overcapacity; existing refineries often operate near or below capacity.
গ) Hydrocracking units are limited; this is not a limiting factor.
ঘ) Jet fuel production is balanced with demand; overproduction is not the issue.

1.In petroleum refining, after atmospheric distillation, the heavier fractions are sent to a vacuum distillation unit to avoid thermal cracking.
2.Vacuum distillation products:
Vacuum gas oil (VGO): Medium-heavy fraction, typically 370–550°C boiling range, used as feedstock for catalytic cracking to produce lighter fuels like gasoline and diesel.
Asphalt/residuum: Heavier fraction used for road construction.

Other options:
Straight-run gasoline → already light and does not require cracking.
Asphalt → too heavy for catalytic cracking.
Light naphtha → used for reforming, not cracking.

Catalytic reforming converts low-octane naphtha into high-octane reformate.
Key reactions include:
Dehydrocyclization: Linear or branched paraffins are converted into aromatics (e.g., hexane → benzene, heptane → toluene).
Aromatics have high octane numbers, boosting gasoline quality.
Dehydrogenation of naphthenes: Cycloalkanes → aromatics.
Isomerization: Straight-chain paraffins → branched paraffins (also raises octane).

Other options:
ক) Isomerization improves octane but does not produce aromatics.
গ) Hydrogenation saturates double bonds; lowers octane.
ঘ) Alkylation combines small olefins with isoparaffins; it produces high-octane components, but not via aromatic formation.

Hydrocracking is a catalytic process performed in the presence of hydrogen, which:
Cracks heavy feedstocks into lighter fractions.
Saturates aromatics and olefins, producing stable, low-sulfur products.
It is ideal for producing middle distillates like:
Kerosene (jet fuel)
Diesel (high-quality, low-sulfur)

Other options:
খ) LPG and gasoline are mainly produced via catalytic cracking.
গ) High-octane gasoline is also a product of reforming and cracking.
ঘ) Heavy fuel oils are the residuals; hydrocracking converts them to lighter fractions.

1.Catalytic cracking units (FCC) crack heavy hydrocarbons into lighter products like gasoline and LPG.
2.Coke formation is a natural byproduct, which can deactivate the catalyst.
3.To minimize coke:
High catalyst-to-oil ratio → ensures sufficient active sites for cracking without over-cracking to coke.
Continuous catalyst regeneration → burns off deposited coke, maintaining catalyst activity.

Other options:
ক) Very low temperatures reduce cracking efficiency but do not prevent coke formation effectively.
খ) Hydrogen presence is not critical in FCC; hydrocracking uses hydrogen to suppress coke.
ঘ) Reactor pressure is controlled; vacuum is not relevant to FCC coke prevention.

1.Gorilla Glass is an aluminosilicate glass engineered for high strength and scratch resistance.
2.The key process is ion exchange:
Sodium ions (Na⁺) in the glass are replaced with larger potassium ions (K⁺) by immersion in a molten potassium salt bath.
The larger K⁺ ions create compressive stress on the glass surface, which:
Inhibits crack initiation and propagation
Increases resistance to scratches and impacts

Other options:
ক) B₂O₃ lowers thermal expansion but does not significantly increase strength.
গ) PbO increases density and refractive index (lead glass), not scratch resistance.
ঘ) MgO/CaO addition for crystallization is used in ceramics/glass-ceramics, not Gorilla Glass.

1.Silicon nitride (Si₃N₄) is a high-strength, high-temperature ceramic used in cutting tools.
2.Sintering aids like Y₂O₃ and Al₂O₃ are added in small amounts to:
Form a transient liquid phase at the grain boundaries during sintering.
Enhance particle rearrangement and densification, resulting in near-full density.
Improve mechanical properties such as toughness and strength.

Other options:
ক) Hardness is not reduced; thermal conductivity is only slightly affected.
গ) The goal is not to increase the amorphous phase; excessive amorphous content can weaken the ceramic.
ঘ) Grain boundary oxidation is a concern, but sintering aids primarily assist densification, not prevent oxidation.

1.Lead glass contains PbO, which:
Increases density → effective at attenuating X-rays
Increases refractive index → used in optical applications like decorative glassware and lenses
2.Applications: X-ray windows, protective shields, and optical lenses

Other options :
খ) Photochromic glass changes color reversibly under UV, mainly for eyewear, not display panels; the change is not permanent.
গ) Aluminosilicate glass is chemically and thermally resistant, often used in smartphone screens and cookware, but it is electrically insulating, not conductive.
ঘ) Fused silica glass has very low thermal expansion and high optical clarity, ideal for optical fibers,

Cement production fundamentally depends on limestone as the primary raw material. Bangladesh has some limestone deposits, but they are limited in quantity and quality. As a result, the country cannot rely entirely on domestic sources to meet its cement demand and must import significant amounts of high-quality limestone.

Other optionst:
ক) Demand for cement is actually high due to rapid urbanization and infrastructure growth.
গ) Overproduction is not the main limiting factor; the industry is still growing.
ঘ) While skilled labor is important, the main bottleneck is raw material availability, not workforce.

A pre-calciner kiln system is an advanced type of cement kiln where a large portion of the fuel is used in a separate pre-calciner before the kiln. This has several advantages over traditional dry-process kilns:
Higher thermal efficiency: More of the limestone is calcined before entering the rotary kiln, reducing fuel consumption.
Increased production capacity: Since calcination happens partially outside the kiln, the kiln can operate faster.
Better temperature control: Improves clinker quality and allows for higher throughput.

Other options:
ক) Pre-calciner kilns actually improve clinker quality, not lower it.
খ) Raw material still needs grinding; pre-calciner doesn’t eliminate this step.
ঘ) Lime saturation factor is a raw mix parameter, not a direct requirement of pre-calciner systems.

In Portland cement:
1.Dicalcium silicate (C₂S) hydrates more slowly than tricalcium silicate (C₃S).
2.It contributes mainly to the later strength development, typically noticeable from 7 days onward, and is most significant in the 28–90 day range.
3.Early strength (1–3 days) is largely due to C₃S, not C₂S.
4.C₂S has little effect on setting time or gypsum interactions.

In the diaphragm cell process for chlor-alkali production:
1.The anode produces chlorine gas (Cl₂).
2.The cathode produces sodium hydroxide (NaOH) and hydrogen (H₂).
3.A porous asbestos diaphragm separates the two compartments.
It allows ions (mainly Na⁺ and OH⁻) to migrate through the pores.
It prevents bulk mixing of Cl₂ and NaOH solutions, avoiding dangerous reactions.

Other options:
খ) Describes a membrane cell (modern, not diaphragm cell).
গ) Refers to the mercury cell process.
ঘ) Mechanical stirring cannot effectively prevent mixing of products.

1.Cation-exchange membranes allow Na⁺ ions to pass from the anode (brine) compartment to the cathode compartment while blocking Cl⁻ ions.
2.However, water can diffuse back from the cathode compartment to the anode (osmosis and electro-osmosis), which limits the achievable NaOH concentration.
3.Typically, this limits NaOH production to about 30–32 wt%.

Other options:
ক) Temperature of the feed affects efficiency but is not the primary limiting factor.
গ) Chlorine solubility does not significantly limit NaOH concentration.
ঘ) Precipitation of NaCl occurs only in extreme conditions and is not the main limitation.

The caustic soda–chlorine industry relies heavily on high-purity salt (NaCl) as the feedstock. In Bangladesh:
1.Domestic salt production is limited in quantity and often contains impurities that reduce the efficiency and lifespan of electrolytic cells.
2.Importing high-purity salt increases production costs.

Other options:
খ) There is a growing market for chlorine derivatives, so demand is not the main limitation.
গ) Environmental regulations exist, but modern technologies (membrane cells) mitigate mercury issues.
ঘ) Electricity supply is actually a constraint, not an excess.

The mercury cell process for producing caustic soda and chlorine uses a liquid mercury cathode. Major environmental concerns include:
1.Mercury loss and spillage, which can contaminate water bodies and soil.
2.Mercury is highly toxic, persistent, and bioaccumulative, posing serious environmental and health risks.

Other options :
ক) CO₂ emissions are not a major concern in this process.
খ) Ammonia is not a typical emission from mercury cells.
ঘ) Sodium sulfite is not a primary waste in mercury cells.

Polypropylene (PP) has a methyl group (-CH₃) on every other carbon of the backbone.
This adds steric hindrance, which:
1.Increases crystallinity and melting point (PP melts around 160–170°C, while HDPE melts around 130–135°C).
2.Improves thermal resistance compared to polyethylene (PE).

Other options:
ক) PP actually has a higher, not lower, melting point than HDPE.
খ) PP and PE do not have identical thermal properties.
ঘ) PE is less thermally stable than PP; branching reduces crystallinity and melting point.

1.Polymethylacrylate (PMMA) is a highly transparent polymer.
2.Its amorphous structure (i.e., lack of crystalline regions) allows light to pass through with minimal scattering, giving it clarity similar to glass.
3.Crystalline regions would scatter light and reduce transparency.

Other options :
ক) Plasticizers may improve flexibility but do not inherently increase transparency.
খ) PMMA does not incorporate phenyl groups; that is polystyrene (PS).
গ) High crystallinity reduces transparency, not increases it.

1.High-density polyethylene (HDPE) is mostly linear with minimal branching, allowing the polymer chains to pack closely. This results in:
Higher crystallinity
Higher density
Greater tensile strength and stiffness
2.Low-density polyethylene (LDPE) is highly branched, which:
Reduces chain packing
Lowers crystallinity and density
Makes it more flexible but mechanically weaker

Other options :
খ) Branching significantly affects mechanical properties.
গ) HDPE has less branching, not more.
ঘ) LDPE’s high branching reduces, not increases, crystallinity and melting point.

The pulp and paper industry generates significant environmental pollution, including:
1.Chlorinated organic compounds from conventional chlorine bleaching (toxic to aquatic life)
2.High water usage leading to wastewater discharge
3.Solid and chemical wastes
Key measures to reduce environmental impact include:
1.Chlorine-free bleaching (e.g., oxygen, ozone, or chlorine dioxide) to minimize toxic organics.
2.Recycling process water to reduce water consumption and effluent volume.
3.Proper effluent treatment to remove solids, chemicals, and color before discharge.

Other options:
খ) Mercury-based catalysts are toxic and environmentally hazardous.
গ) Reducing cellulose content compromises product quality and doesn’t help pollution.
ঘ) Energy recovery systems reduce CO₂ and other emissions, so eliminating them is undesirable.

The key difference between viscose and cuprammonium rayon lies in their cellulose dissolution processes:
Viscose rayon:
1.Cellulose is treated with sodium hydroxide (NaOH) to form alkali cellulose.
2.Reacted with carbon disulfide (CS₂) to form cellulose xanthate.
3.Dissolved in dilute NaOH to produce a viscous solution for fiber spinning.
Cuprammonium rayon:
1.Cellulose is dissolved directly in a cuprammonium solution (copper-ammonia complex).
2.This solution is then spun into fibers.

Other options :
খ) Tensile strength varies but is not the defining difference.
গ) Viscose rayon requires chemical treatment, so this is false.
ঘ) Cuprammonium rayon can be spun into fibers; that’s its main purpose.

1.Kraft pulp is produced using the sodium hydroxide/sodium sulfide process, which effectively removes lignin while preserving the cellulose fibers.
2.The resulting fibers are:
Longer and stronger, enabling better fiber-to-fiber bonding.
Higher in cellulose content, which is crucial for tensile strength.
3.This makes Kraft pulp ideal for high-strength paper such as packaging, sacks, and industrial-grade papers.

Other options :
ক) Kraft fibers are generally longer, not shorter.
খ) Kraft pulp removes most lignin; retaining lignin would actually reduce strength.
ঘ) While cost and environmental impact differ, the primary reason for preference is fiber strength and cellulose purity, not cost alone.

1.In soap production, glycerine is produced as a byproduct during saponification of fats or oils.
2.Glycerine is highly soluble in water, which means:
Recovering it from the aqueous phase requires energy-intensive processes, such as evaporation or distillation.
3.This high water solubility is the main challenge in glycerine recovery.

Other options:
ক) Glycerine does not form insoluble salts with fatty acids under normal conditions.
খ) Glycerine is stable at room temperature; decomposition is not an issue.
ঘ) Alkali is required for soap formation; it does not prevent glycerine formation.

1.In synthetic detergent production, sulfonation of organic compounds (like linear alkylbenzene) produces sulfonic acids.
2.These acids are not water-soluble in their acidic form.
3.Neutralization with alkali (e.g., NaOH or KOH):
Converts the sulfonic acid into its salt form (e.g., sodium or potassium sulfonate).
Ensures the detergent is water-soluble and safe for use in cleaning applications.

Other options :
খ) While neutralization adjusts pH, its main purpose is forming the salt, not merely removing residual alkali.
গ) Crystallization is not typically involved for liquid detergents.
ঘ) Glycerine separation is relevant in soap, not synthetic detergents.

1.In industrial saponification, fats and oils are reacted with alkali (NaOH or KOH) to produce soap and glycerine.
2.Using a slight excess of alkali ensures:
Complete saponification of all triglycerides.
Minimization of unreacted fat, which can lead to rancidity and spoilage.
3.This practice improves soap quality and shelf life.

Other options :
ক) Alkali does not affect cooling.
খ) Excess alkali does not reduce glycerine; glycerine yield is determined by fat content.
গ) Soap hardness is mainly influenced by type of fatty acid and curing, not excess alkali.

1.Vegetable tanning uses tannins from plant sources (like bark, wood, or leaves) to convert raw hides into leather.
2.This produces firm, durable leather with:
High tensile strength
Good dimensional stability
A characteristic brown color that can age beautifully
3.Such leather is ideal for heavy-duty applications like belts, saddles, harnesses, and work boots.

Other options :
খ) Waterproof jackets are usually made from chrome-tanned leather or treated fabrics.
গ) Synthetic leather substitutes are man-made, not vegetable-tanned.
ঘ) Chrome-tanned leather is soft, flexible, and suited for upholstery, not vegetable-tanned leather.

1.In leather processing, the liming step involves soaking hides in a calcium hydroxide (lime) solution, often with sodium sulfide.
2.The main purposes are:
Swelling and opening up the collagen structure
Loosening and removing hair, epidermis, and some proteins from the hide
3.This prepares the hide for further processing such as tanning.

Other options :
ক) Softening occurs later, during tanning and mechanical working, not liming.
গ) Coloring happens in dyeing or finishing, not liming.
ঘ) Stabilization of collagen fibers is achieved during tanning, not liming.

1.Chrome-tanned leather is treated with chromium salts (mainly chromium(III) sulfate), which crosslinks the collagen fibers differently from vegetable tannins.
2.Advantages of chrome tanning:
1.Faster processing (tanning can be completed in a day vs. weeks for vegetable tanning)
2.Higher flexibility and softness
3.Better water resistance and durability
4.Good dye uptake

Other options :
ক) Chrome tanning is actually faster, not longer.
গ) Chrome tanning uses chemical salts, not only natural materials.
ঘ) Chrome-tanned leather can be dyed easily, unlike the statement.

1.Hydrogenation is the addition of hydrogen to the carbon–carbon double bonds (unsaturated bonds) in fatty acids.
2.Effect of higher degree of hydrogenation:
More double bonds are saturated → fatty acids become more saturated.
Oil becomes more solid or semi-solid at room temperature.
Shelf life improves → less prone to oxidation and rancidity.

Other options:
ক) More liquid oils → Wrong; hydrogenation reduces fluidity, making oil more solid.
গ) Lower melting point → Wrong; hydrogenation increases melting point due to saturation.
ঘ) Increased iodine value → Wrong; iodine value decreases as unsaturation decreases.

Partial Hydrogenation:
1.In partial hydrogenation, only some of the double bonds in unsaturated fatty acids are saturated.
2.During this process, cis double bonds can isomerize to trans configuration, forming trans-fatty acids.
Implications of Trans-Fatty Acids:
1.Increase the solidification of oils (desired for margarine and shortening).
2.Health concern: High intake is associated with cardiovascular diseases.

Other options:
খ) Cis-unsaturated fatty acids → Already present in natural oils; partial hydrogenation converts some cis to trans.
গ) Free fatty acids → Not a primary product; FFA are removed during refining, not formed during hydrogenation.
ঘ) Wax esters → Not formed in hydrogenation; wax esters come from wax-producing plants or chemical esterification.

Nickel is the most commonly used catalyst because:
1.It is active and selective for hydrogen addition to double bonds.
2.It is economical and widely available.
3.Provides controlled hydrogenation to achieve partial or full saturation.

Other options:
খ) Copper → Not effective for hydrogenation; mainly used in electrical and decorative applications.
গ) Iron → Not active for hydrogenation of oils.
ঘ) Platinum → Expensive; used in specialty hydrogenation reactions, not large-scale edible oil processing.

Improve flow and leveling → smoother surface during application.
Control drying rate → prevent cracking or uneven finish.
Increase durability → resistance to UV, moisture, or chemical attack.
Prevent defects → such as foaming, sedimentation, or microbial growth.

Other options:
ক) Reduce cost only → Some additives may reduce cost slightly, but their primary purpose is property enhancement.
গ) Provide pigment → Pigments are separate from additives; they provide color and opacity.
ঘ) Replace the binder → Binders form the film and adhesion; additives do not replace binders.

Milling is the process of grinding pigments into the liquid medium (binder + solvent) to produce a uniform paint.
Purpose:
Disperse pigments evenly → ensures consistent color and opacity.
Reduce particle size → improves paint stability, gloss, and surface finish.
Enhance performance → better adhesion and coverage.

Methods of Milling:
Ball mill → rotating cylinder with steel balls crushes pigment particles.
Sand mill → uses sand as grinding medium for finer dispersions.
High-speed dispersers → for smaller batch operations.

Oil-Based Paints:
1.Made from drying oils (like linseed oil) and pigments.
2.Drying mechanism:
1.The oil undergoes slow oxidation when exposed to air.
2.Forms a hard, durable, and protective film over the surface.
Properties:
1.Good adhesion and durability.
2.Provides a glossy finish.
3.Long drying time compared to enamel or water-based paints.