If the bromine atom is available in the form of, say, two isotopes ₃₅⁷⁹Br (49.7%) and ₃₅⁸¹Br (50.3%), calculate the average atomic mass of bromine atom.

The average atomic mass of a sample of element X is 16.2 u. What are the percentages of isotopes ₈¹⁶X and ₈¹⁸X in the sample?

Composition of the nuclei of two atomic species, X and Y, are given as under

Give the mass numbers of X and Y. What is the relation between the two species?