Question

An element(at. mass z) has a isotopic masses (z+2) and (z-1). Find the percentage abundance of heavier isotope.

Answer 1

let us assume that atoms with atomic mass Z+2 be x%
so that of Z-1 be (100-x)%
now, ((Z+2)*x+(Z-1)*(100-x))/100=Z
i.e. Zx+2x+100Z-Zx-100+x=100Z
i.e. 3x=100
i.e. x=33.33

so the percentage abundance of heavier isotope is 33.33%