Which of the following pairs are isotopes ? Give reasons for your choice :

(i) ⁵⁸₂₆A, ⁵⁸₂₈B or

(ii) ⁷⁹₃₅X, ⁸⁰₃₅Y

Atoms of the same element can have different numbers of neutrons; the different possible versions of each element are called isotopes.

(ii) 7935X and 8035Y are isotopes as they have same atomic number.