The composition of the nuclei of two atomic species X and Y are given as under Protons = 6(X): 6(Y) Neutrons = 6(X): 8(Y)
Atomic mass of X = Number of protons + Number of neutrons = 6 + 6 = 12.
Atomic mass of Y = Number of protons + Number of neutrons = 6 + 8 = 14.
These two atomic species, X and Y, have the same atomic number but different mass numbers. Hence, they are isotopes.
