Question

The average atomic mass of a sample of an element X is 16.2u. What are the parcentage of isotopes ${}_8^{16}X$ and ${}_8^{18}X$ in the sample?

Answer 1

Given
Average atomic mass $=16.2u.$
${\text{Let, \% of}}^{16}8X=a;{\text{\% of}}_8^{18}X=(100-a)$
Average atomic mass is generally calculated using the formula,
$A_1\times \frac{x}{100}+A_2\times \frac{Y}{100}$
Where,
$A_1,A_2\Rightarrow \text{Atomic masses}$
$X,Y\Rightarrow \text{Respective percentages}$
using the given data,
$16.2=16\times \frac{a}{100}+18\times \frac{100-a}{100}$
$1620=1800-2a$
$a=90\text{\%}{(}_8^{16}X)$
$100-a=10\text{\%}{(}_8^{18}X)$