MCQ
Molality (m) of $3 \mathrm{M}$ aqueous solution of $\mathrm{NaCl}$ is:

(Given : Density of solution $=1.25 \mathrm{~g} \mathrm{~mL}^{-1}$, Molar mass in $\left.\mathrm{g} \mathrm{mol}^{-1}: \mathrm{Na}-23, \mathrm{Cl}-35.5\right)$

  • A
    $2.90 \mathrm{~m}$
  • $2.79 \mathrm{~m}$
  • C
    $1.90 \mathrm{~m}$
  • D
    $3.85 \mathrm{~m}$

Answer

Correct option: B.
$2.79 \mathrm{~m}$
b
$3$ moles are present in $1$ litre solution

$\text { molality }=\frac{3 \times 1000}{1.25 \times 1000-[3 \times 58.5]}=2.79 \mathrm{~m}$

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