Chemistry - Mole Concept Question with Solution | TestHub

Let the relative abundance of ${}^{35}\mathrm{Cl}$ be $x$ and that of ${}^{37}\mathrm{Cl}$ be $y$.

The average atomic mass is given by:

$\text{Average atomic mass}=\frac{35x+37y}{x+y}$

Given that the average atomic mass is $35.5$:

$\frac{35x+37y}{x+y}=35.5$

$35x+37y=35.5x+35.5y$

$1.5y=0.5x$

$\frac{x}{y}=\frac{1.5}{0.5}=\frac{3}{1}$

The ratio of their relative abundance is $3:1$.

Answer: $3:1$