In which one of the following all the concentration terms are independent of temperature?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → mole fraction, mass fraction, molality
A concentration term changes with temperature only if it contains the volume of the solution, because liquids expand on heating while their mass does not change.
Mole fraction, mass fraction and molality use only masses and moles, while molarity uses the volume of the solution:
\( \displaystyle \text{molality} = \frac{\text{moles of solute}}{\text{mass of solvent (kg)}} \qquad \text{molarity} = \frac{\text{moles of solute}}{\text{volume of solution (L)}} \)
So the set in which every term is independent of temperature is mole fraction, mass fraction, molality.
Shortcut: Options (1), (2) and (3) all contain molarity, the one volume-based term, so only Option (4) is left.
NCERT (2026-27 edition):
Expressing Concentration of Solutions – …
