৪৯তম বিসিএস ⎯ রসায়ন [৫৩১]

Colligative properties of solutions are physical properties that depend solely on the number of solute particles in a solution, not their identity. These properties include: 
lowering of vapor pressure,
elevation of boiling point,
depression of freezing point
osmotic pressure

ΔT_f means freezing point depression which is a colligative property. So the answer is C


Source: Any text book or relevant sites

Source: Any text book or relevant sites

Standard oxidation potential (E⁰_ox) is a measure of how readily a chemical species loses electrons (i.e., gets oxidized) under standard conditions (usually 298 K, 1 atm, and 1 M concentration)

Standard reduction potential (E⁰_red) is a measure of a chemical species' tendency to gain electrons (be reduced) under standard conditions

Cell potential, also known as electromotive force (EMF), represents the driving force that pushes electrons from the anode (where oxidation occurs) to the cathode (where reduction occurs)

E⁰_cell= E⁰_ox+E⁰_red=0.76+0.80 V=1.56V

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An oxidation half-reaction is one of the two components of a redox reaction are  oxidation half-reaction & reduction half reaction. 

An oxidation half-reaction is the process where a chemical species loses electrons and its oxidation number increases & it occurs in anode. On the other hand, A reduction half-reaction is a chemical species gains electrons and its oxidation number decreases. This process is the opposite of oxidation. So, it occurs in cathode.

Here, oxidation Half Reaction: Sn²⁺ → Sn⁴⁺ +2e-
As oxidation occurs in anode, so the answer is C

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If we consider the reaction, Sn⁴⁺ → Sn²⁺ + 2e-;
Then the nernst equation becomes  E_red =E⁰_red - 0.059/2 log ([ Sn2+ ]/[Sn4+])=E⁰_red - 0.03
So, the right answer is B


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A. Depend on number of particles, not identity — correct.

B. Van’t Hoff factor i is always greater than 1 for all solutes — incorrect. Non-electrolytes have i=1; association can make i<1 ; electrolytes can have i>1 but not universally.

C. Boiling point elevation ∝ molality — correct 

D. Osmotic pressure can be used to determine molar mass — correct (π = i MRT for dilute solutions).


Source: Any text book or relevant sites

Source: Any text book or relevant sites

For pure water C=1

At the triple point three phases coexist (ice, liquid water, vapor) so P=3

F= C-P+2=1-3+2=0


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In an electrochemical cell, cell potential (or cell voltage) is the measure of the electrical potential difference between the two electrodes.

Ionization potential, also known as ionization energy, is the minimum energy required to remove an electron from a gaseous atom or ion.

Standard reduction potential is a measure of a chemical species' tendency to gain electrons (be reduced) under standard conditions.

Polarization potential, in electrochemistry  refers to the deviation of a system's potential from its equilibrium value due to the flow of current or other factors

So, the answer is A

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A good reference electrode maintains a constant and well-defined potential, even when the surrounding conditions change slightly. Standard hydrogen electrode has a standard potential of 0 V by definition. 

The other electrodes do not have a standard potential of 0 V by definition. So, the answer is B

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In a galvanic/electrochemical cell, the anode is: negative
In a electrolytic cell, the anode is: positive

So, the answer is B


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π=i MRT
Here,  π = osmotic pressure
i = the van 't Hoff factor  
M= Concentration in Molarity
R= Ideal gas constant
T= absolute temperature

So, i=3.03 (Assuming, m=M)

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For most substances, higher pressure raises melting point, but ice is an exception because water’s solid phase is less dense than its liquid phase; increasing pressure actually lowers the melting point. So the answer is C.


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The phase rule was first discovered by Josiah Willard Gibbs. He developed this fundamental concept in thermodynamics in the 1870s. The phase rule describes the relationship between the number of phases, components, and degrees of freedom in a system at equilibrium.


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A saturated solution of sodium chloride consists of:
Solid NaCl (undissolved crystals) & Liquid solution (water + dissolved NaCl)
That’s two distinct phases: one solid phase, one liquid phase


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A real solution is one that shows deviations from ideal behavior, meaning it does not obey Raoult’s law over the whole concentration range.


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​The elevation in boiling point is given by the formula where K_β means all of these.

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Vapour Pressure Lowering (Raoult’s Law)

When a non-volatile solute is added to a solvent, the vapor pressure of the solution decreases compared to the pure solvent. The relative lowering of vapor pressure is equal to the mole fraction of solute. Adding a non-volatile solute to a solvent lowers its vapour pressure because fewer solvent molecules can escape into the vapour phase.

So, the answer is B


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Triple point means the temperature and pressure at which the solid, liquid, and vapour phases of a pure substance can coexist in equilibrium.

At the triple point, temperature and pressure are both fixed for a given substance — it’s the unique condition where solid, liquid, and gas phases coexist in equilibrium.

So, the answer is A


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Isomerism is a phenomenon where two or more molecules have the same molecular formula but different chemical structures.

Racemization is a chemical process that converts an optically active compound into a racemic mixture

Polymorphism is the ability of a substance to exist in two or more distinct crystalline forms while maintaining the same chemical composition.

So, the answer is C

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সঠিক উত্তর: (Ps - P)/Ps
​অপশনে সঠিক উত্তর না থাকায় প্রশ্নটি বাতিল করা হলো। 
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​Vapour Pressure Lowering (Raoult’s Law)

When a non-volatile solute is added to a solvent, the vapor pressure of the solution decreases compared to the pure solvent. The relative lowering of vapor pressure is equal to the mole fraction of solute.  

The relative lowering of vapor pressure is represented by the ratio of the decrease in vapor pressure to the vapor pressure of the pure solvent that is (Pₛ - P)/P_S


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In the water system, which includes ice, liquid water, and water vapor, there is only one component. This is because all three phases can be represented by the chemical formula H₂O

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