(i) Atomic mass of elements ‘X’ = Number of protons + Number of neutrons
= 8 + 8 = 16 u
(ii) Atomic mass of element ‘Y’ = Number of neutrons + Number of protons
= 10 + 8 = 18 u
Relationship between X and Y: The atomic number of the elements is same but their atomic masses are different. Hence, they are isotopes of each other.