Question

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

(i) `""_26^58"A"`,  `""_28^58"B"` or (ii) `""_35^79"X"`,  `""_35^80"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"A"_58` and `""^58"B"_28` are not isotopes because they have different atomic numbers.
(ii)`""^79"X"_35` and `""^80"Y"_35` are isotopes as they have same atomic number.