Liquid State

Colligative properties are used to determine the molar mass of the solute, not the solvent. Check statements:

• (A) is incorrect.
• (B) is correct.
• (C) is correct.
• (D) is correct.
• (E) is correct.

Hence, the incorrect statement is:

The van’t Hoff factor tells the effective number of particles in solution. Strong electrolytes like , , and dissociate almost completely into 2 ions, so is close to 2. dissociates into 3 ions, so is closer to 3. But is known to show incomplete dissociation and ion pairing in solution, so its can be less than 2, such as 1.82.
Hence, the correct answer is:

Use osmotic pressure formula: So, Given: Taking , substitute:
Hence, the correct answer is:

Concept:
Some organic liquids have very high boiling points and may decompose before reaching their normal boiling temperature.
Step 1: Understand boiling point effect.
A liquid boils when its vapour pressure becomes equal to external pressure.
Step 2: Reduce external pressure.
If pressure is reduced, the liquid boils at a lower temperature. Therefore decomposition can be avoided.
Step 3: Choose correct purification method.
The process of distillation at low pressure is called: It is also known as vacuum distillation.
Step 4: Final answer.

Hence, correct option is (D).

Concept: Chemistry - Depression in Freezing Point. [ \Delta T_f = K_f \times m ] where = molality.
Step 1: Find molality. [ m=\frac{\Delta T_f}{K_f}=\frac{2.5}{5}=0.5 ]
Step 2: Use molality formula. [ m=\frac{\text{moles of solute}}{\text{kg of solvent}} ] Mass of benzene: [ 25g=0.025kg ] So moles of benzoic acid: [ \text{moles}=0.5 \times 0.025=0.0125 ]
Step 3: Calculate molar mass. [ \text{Molar mass}=\frac{\text{mass}}{\text{moles}}=\frac{3}{0.0125}=240 ]
Step 4: Final answer. [ \boxed{240\text{ g mol}^{-1}} ]
Hence, correct option is (C).