Question

Element X consists of two isotopes with masses of 62.9 and 64.9.

The relative atomic mass of the element is 63.6. The percentage
abundance of the lighter isotope is closest to -
Select one:
-65%

-55%

-35%

-45%

Answer 1

65%.

Step-by-step explanation:

If the abundance of the lighter isotope is x then the abundance of the heavier isotope is 1-x. So:

62.9x + 64.9(1 - x) = 63.6

62.9x - 64.9x = 63.6 - 64.9

-2x = -1.3

x = 0.65 or 65%.