Question

An element has two isotopes, A and B, with mass numbers of 32.0 and 33.0 respectively. The relative atomic mass is 32.3. The percentage abundance of the two isotopes is:

a) A - 20% B - 80%

b) A - 25% B - 75%

c) A - 80% B - 20%

d) A - 70% B - 30%

e) A - 50% B - 50%

Answer 1

Answer:

d) A - 70% B - 30%

Explanation:

If x is the abundance of A, and 1−x is the abundance of B, then:

x (32.0) + (1−x) (33.0) = 32.3

32x + 33 − 33x = 32.3

33 − x = 32.3

x = 0.7

The abundance of A is 70%, and the abundance of B is 30%.

Answer 2

D is the correct answer