Question

A $5\%$ solution of cane sugar (mol. mass = $342$) is isotonic with $1\%$ solution of a substance $X$. The molecular mass of $X$ is:

• A. $34.2$
• B. $171.2$
• C. $68.4$
• D. $136.8$

Answer 1

The correct option is C $68.4$

$\begin{array}{c}\text{Given}5\%\text{solution of Cane Sugar}\\ \Rightarrow 5g\text{of solute present in}100ml\text{of solution}\\ \\ \text{For isotonic solutions}{\pi }_1={\pi }_2\\ \Rightarrow c_1=c_2\end{array}$

$\begin{array}{c}\frac{5}{342\times 0.1}=\frac{1}{M_2\times 0.1}\\ \\ \Rightarrow M_2=\frac{342}{5}=68.4\\ \\ \text{Hence option}C\text{is correct}\end{array}$