Some Basic Concepts of Chemistry - Result Question 11 — JEE PYQ Chapterwise

Answer:

Correct Answer: 11. (b)

Solution:

Molality $(m)=\dfrac{\text { Number of moles of solute }}{\text { Mass of solvent (in g) }} \times 1000$

$\begin{aligned} & =\dfrac{\text { Mass of solute }(\text { in } g) \times 1000}{\begin{array}{r} \text { Molecular weight of solute } \times \text { mass of solvent }(\text { in } g) \end{array}} \\ & =\dfrac{w _{Na^{+}} \times 1000}{M _{Na^{+}} \times w _{H _2 O}}=\dfrac{92 \times 1000}{23 \times 1000}=4 mol kg^{-1} \end{aligned}$