Question

Chlorine exists in two isotopic forms, $Cl-37$ and $Cl-35$ but its atomic mass is $35.5$. This indicates the ratio of $Cl-37$ and $Cl-35$ is approximately

• A. $1 : 2$
• B. $1 : 4$
• C. $1 : 3$
• D. $3 : 1$

Answer 1

Answer: (C)

$1 : 3$

Answer 2

The correct answer is Option C) $1 : 3$

Let the relative abundance of $Cl-37 = x\%$ then the relative abundance of $Cl-35 = (100 - x)\%$

Average atomic mass $=\frac{x \times 37+\left(100-x\right)35}{100}$ $=35.5$ $\Rightarrow 37x+3500-35x$ $=3550 \Rightarrow x=25$ $\therefore 100-x=75$

Thus, the ratio of $Cl-37$ and $Cl-35$ is $x$ : $(100 - x)$ $=25 : 75$ $1 : 3$

Read more from the chapter:**Structure of Atom **