The average atomic mass of a sample of an element X is 16.2 u, what are the percentages of isotopes `"_8^16X` and `"_8^18X` in the sample?

Explanation

Let , the percentage of `""_(8)^(16) X` in the sample be x . Then the percentage of `""_(16) ^(8) X` in the sample is (100 - x) . Then
Atomic mass of X = `16 xx ((x)/(100)) + 18 xx ((100 - x)/(100))`
`16.2 = (16 x)/(100) + (18 xx 100)/(100) - (18 x)/(100)`
`1620 = 16 x - 18 x + 1800`
or , `2 x = (1800 - 1620) = 180`
Thus , `x = 180//2 = 90`
Percentage of `""_(8)^(16) X` in the sample = 90
Percentage of `""_(8)^(18) X` in the sample = 10 .