Question

Chlorine has two naturally occurring isotopes, ${ }^{35} Cl$ and ${ }^{37} Cl$. If the atomic mass of $Cl$ is $35.45$, the ratio of natural abundance of ${ }^{35} Cl$ and ${ }^{37} Cl$ is closest to

• A. 3.5 : 1
• B. 3 : 1
• C. 2.5 : 1
• D. 4 : 1

Answer 1

Answer: (B)

Let the natural abundance of ${ }^{35} Cl$ be $x$.
Let the natural abundance of ${ }^{37} Cl$ be $y$.
$M_{ av }=\frac{M_{x} x+M_{y} y}{x+y}$
$35.45=\frac{35 x+37 y}{x+y} $
$\therefore \frac{x}{y}=\frac{3}{1}$