' x ' g of NaCl is added to water in a beaker with a lid. The temperature of the system is raised from…

' x ' g of NaCl is added to water in a beaker with a lid. The temperature of the system is raised from $1^{\circ} \mathrm{C}$ to $25^{\circ} \mathrm{C}$. 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]




Solution

$\underset{1^{\circ} \mathrm{C}}{\text { Water }} \xrightarrow[\text { decreases }]{\text { Volume }}\underset{4^{\circ} \mathrm{C}}{\text { Water }} \xrightarrow[\text { thermal expansion }]{\text { Volume increases }} \underset{25^{\circ} \mathrm{C}}{\text { Water }}$ Water
$\text { Molarity }=\frac{\mathrm{n}_{\text {solute }}}{(\text { Volume of solution })_{\ell}}$
Hence
$1^{\circ} \mathrm{C} \xrightarrow[\text { increases }]{\text { molarity }} 4^{\circ} \mathrm{C} \xrightarrow[\text { decreases }]{\text { molarity }} 25^{\circ} \mathrm{C}$

Asked in: JEE Main 2025 (02 Apr Shift 2)

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