Question

An element 'A' has 3 natural isotopes 20A, 21A, 22A. If average atomic
mass of 'A' is 21.15 and percentage abundance of 20A is 30% then
percentage abundance of 21A will be
(1)25 %
(2)40 %
(3)70 %
(4)80 %​

Answer 1

Answer:

1) 25%

Here's the solution.