JAMB Chemistry 1980 Question 25

Question 25

Atomic Structure

Given the mean atomic mass of chlorine prepared in the laboratory to be 35.5 and assuming that chlorine contains two isotopes of mass number 35 and 37, what is the percentage composition of the isotope of mass number 35?

A.20
B.25
C.50
D.75
E.90

Show the answer and explanation

Answer: D (75)

Explanation

Let x% be Cl-35: 35x + 37(100 − x) = 3550, so 2x = 150 and x = 75%.