Question

An element has 2 isotopes with mass numbers 16 and 18 . The average atomic wieight is 16.5. THe percentage abundance of these isotopes is _____ and ________ respectively .

Answer 1

let the composition of 1st isotope= x%

so the composition of 2nd isotope =(100-x)%

Now we know that..

16.5 = 16 x (0.0X)+18 x (1-0.00X)

Solving we get..

X =75

so, 1-X= 25

And hence the composition is 75% and 25%.