Question

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

(i) ${}_{26}{}^{58}\mathrm{A},{}_{28}{}^{58}\mathrm{B}$ or (ii) ${}_{35}{}^{79}\mathrm{X},{}_{35}{}^{80}\mathrm{Y}$

Answer 1

(i) Atoms of the same element can have different numbers of neutrons; the different possible versions of each element are called isotopes. ${}^{58}\mathrm{A}_{26}$ and ${}^{58}\mathrm{B}_{28}$ are not isotopes because they have different atomic numbers.
(ii) ${}^{79}\mathrm{X}_{35}$and ${}^{80}\mathrm{Y}_{35}$ are isotopes as they have same atomic number.