Density of 3 M NaCl solution is $1.25 \mathrm{~g} / \mathrm{mL}$. The molality of the solution is :

Density of 3 M NaCl solution is $1.25 \mathrm{~g} / \mathrm{mL}$. The molality of the solution is :
  1. 1.79 m
  2. 2.79 m
  3. 2 m
  4. 3 m

Solution

$\begin{aligned} & 3 \mathrm{M~} \mathrm{NaCl}, \mathrm{d}_{\text {sol }}=1.25 \mathrm{gm} / \mathrm{mol} \\ & \begin{aligned} \text { Molality } & =\frac{\mathrm{M} \times 1000}{1000 \mathrm{~d}-\mathrm{M} \times \mathrm{M}_{\mathrm{W}}} \\ & =\frac{3000}{1250-175.5}=2.79\end{aligned}\end{aligned}$

Asked in: JEE Main 2025 (22 Jan Shift 2)

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