JEE Chemistry 2024 Question with Solution

Given: The options are Molarity, Mass percentage, Molality, and Mole fraction.

Find: Which quantity changes with temperature.

Molarity is defined as

$$M = \frac{n}{V}$$

where $n$ is the number of moles of solute and $V$ is the volume of solution.

Since volume changes with temperature due to thermal expansion or contraction, molarity changes with temperature.

Mass percentage depends on mass, molality depends on mass of solvent, and mole fraction depends on moles. These do not change with temperature in the usual sense.

Therefore, the correct answer is Molarity. The correct option is A.

The solution shows a contradictory heading stating option C, but the worked explanation clearly concludes Molarity, which corresponds to A in the given options.

Given: One option is based on volume, while the others are based on mass or moles.

Find: Which concentration term is temperature-dependent.

Use the shortcut: any concentration term involving volume changes with temperature because liquids expand or contract.

Molarity uses volume:

$$M = \frac{n}{V}$$

Molality, mass percentage, and mole fraction do not involve volume in their definitions.

Therefore, the correct option is A.