Question

Naturally occurring chlorine consists of two isotopes whose atomic weights are 35 and 37. The atomic weight of natural chlorine is 35.5, then what is the ratio of $C{l}^{35}toC{l}^{37}$?

• A. 1 : 3
• B. 3 : 1
• C. 2 : 1
• D. 1 : 2

Answer 1

The correct option is B

3 : 1

Let us consider the sum of percent abundance of $C{l}^{35}$ and $C{l}^{37}$ is equal to 100
So abundance of $C{l}^{35}$ is x and for $C{l}^{37}$ is 100-x
Atomic weight of $C{l}^{35}$ =34.96
Atomic weight of $C{l}^{37}$ =36.96
Atomic weight of $Cl$ =35.45
Average atomic mass=$\frac{34.9689\left(x\right)+36.9695(100-x)}{100}=35.45$
From here x= 76%
Abundance of $C{l}^{35}$ = 76%
Abundance of $C{l}^{37}$ = 24%

Hence, the ratio of $C{l}^{35}$ and $C{l}^{37}$ is 3:1 (approx.)