Question

find the relative abundance of a hypothetical atom of x32 and x34 it is given that average atomic mass is 32.5​

Answer 1

Take the atomic mass of each isotope and multiply by the fractional abundance of that isotope. Then add them all together to get the average atomic mass. For example, Cl has 2 stable isotopes, Cl-35 and Cl-37. Their masses are resp. 34.96885 and 36.96590 and their abundances are resp. 0.7553 and 0.2447. So (34.96885 x 0.7553) + (36.9659 x 0.2447) = ? (The rest is left as an exercise for the reader).