Question

Chlorine has two naturally occuring isotopes ${}_{17}^{37}Cl$ and ${}_{17}^{35}Cl$ and average atomic mass of chlorine is $35.5$. The percentage of ${}_{17}^{37}Cl$ is:

• A. 25%
• B. 75%
• C. 40%
• D. 60%

Answer 1

The correct option is A 25%

Let ,

The percentage of $C{l}^{37}$ be $x$ and The percentage of $C{l}^{37}$ is $y=(100-x)$

Average atomic mass = $\frac{Atomic-mass\times abundance}{100}$

$35.5=\frac{37x+35(100-x)}{100}$

$37x+35(100-x)=3550$

$2x=50$

$\therefore x=25$

$y=100-x=75$

The percentage of $C{l}^{37}$ = 25%

The percentage of $C{l}^{35}$ = 75%

Hence , option A is correct .