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 : 1
• C. 1 : 3
• D. 3 : 1

Answer 1

Answer: (C)

1 : 3

Answer 2

: Let relative abundance of Cl – 37 = x%

then relative abundance of Cl – 35 = (100 –x)%

Average atomic mass,

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

$\Rightarrow$37x+ 3500 – 35 x = 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