PYQ NEET- Organic Chemistry Some Basic Principles L-6

Question: The density of $1 \mathrm{M}$ solution of a compound ’ $\mathrm{X}$ ’ is $1.25 \mathrm{~g} \mathrm{~mL}^{-1}$. The correct option for the molality of solution is (Molar mass of compound $\mathrm{X}=85$ g):#

A) $0.705 \mathrm{~m}$

B) $1.208 \mathrm{~m}$

C) $1.165 \mathrm{~m}$

D) $0.858 \mathrm{~m}$

Answer: $0.858 \mathrm{~m}$#

Solution:#

$$ \begin{alignedat} \mathrm{m} & =\frac{1000 \times \mathrm{M}}{1000 \times \mathrm{d}-\mathrm{MM}_{\mathrm{w}}} \ \mathrm{m} & =\frac{1000 \times 1}{1000 \times 1.25-1 \times 85} \ \mathrm{~m} & =\frac{1000}{1165}=0.858 \end{aligned} $$