Increasing the temperature of an aqueous solution will cause:

The correct answer is Option (2) → Decrease in molarity

Molarity is the number of moles of solute in one litre of solution. On heating, the solution expands: its volume rises while the moles of solute stay the same, so the molarity falls.

Why the other options are incorrect

Option (1) Decrease in molality — Incorrect. Molality is moles of solute per kilogram of solvent; it uses only masses, which do not change with temperature.

Option (3) Decrease in mole fraction — Incorrect. Mole fraction is a ratio of numbers of moles, which heating does not change.

Option (4) Decrease in % (w/w) — Incorrect. Mass percentage is a ratio of two masses, so it does not depend on temperature.

NCERT (2026-27 edition):
1.2 Expressing Concentration of Solutions – “Each method of expressing concentration of the solutions has its own merits and demerits. Mass %, ppm, mole fraction and molality are independent of temperature, whereas molarity is a function of temperature. This is because volume depends on temperature and the mass does not.”