' x ' g of NaCl is added to water in a beaker with a lid. The temperature of the system is raised from 1∘C to 25∘C. Which out of the following plots, is best suited for the change in the molarity ( M ) of the solution with respect to temperature? [Consider the solubility of NaCl remains unchanged over the temperature range]
(A)(see structure)
(B)(see structure)✓ Correct
(C)(see structure)
(D)(see structure)
Answer: (B)
Solution
Molarity is the amount of solute divided by the solution volume, and the dissolved amount stays fixed as the solubility is unchanged. Water reaches its maximum density near 4 °C, so as the temperature rises from 1 °C to 4 °C the solution contracts and the molarity increases, while from 4 °C to 25 °C the solution expands and the molarity decreases. The molarity therefore rises to a maximum at about 4 °C and then falls, matching the plot that peaks near 4 °C before declining.
JEE Main · 2025 · 02 Apr 2025 · Shift 2 · Single correct option
