Question

Relative lowering of vapour pressure is a colligative property because _____________.

• A. It depends on the number of particles of electrolyte solute in a solution and does not depend on the nature of the solute molecules.
• B. It depends on the concentration of a non-electrolyte solute in a solution and does not depend on the nature of the solute molecules.
• C. It depends on the concentration of an electrolyte or a non-electrolyte solute in solution as well as on the nature of solute molecules
• D. It depends on the concentration of a non-electrolyte solute in solution as well as on the nature of the solute molecules.

Answer 1

Answer: (A), (B)

It depends on the concentration of a non-electrolyte solute in a solution and does not depend on the nature of the solute molecules.

Colligative property

Colligative properties are those that depend on the number of solute particles irrespective of their nature.

Analysing the options :

$\left(A\right)$

Relative lowering of vapour pressure is a colligative property as Raoult’s observations established that the lowering of vapour pressure depends only on the concentration of the solute particles and is independent of their identity. Relative lowering of vapour pressure is proportional to the mole fraction of the solute.

The vapour pressure of a solution decreases on the addition of a non-volatile solute and does not depend on the nature of the solute molecules. So, it is a correct statement.

$\left(B\right)$

When electrolytes are dissolved in solution, they are separated into ions. The lowering of vapour pressure does not depend on the nature of electrolyte itself, but on the number of ions. So, it is a correct statement.

As colligative properties are independent of the nature of the solute, options (C) and (D) are incorrect.

Hence, options (A) and (B) are the correct answers.