The isotopes are the elements with same atomic number but different atomic mass or mass number
The mass number is denoted by Z
The mass number is denoted by A
The number of neutrons = N
We know that for an element
A = Z + N
As given the element is indium , its atomic number = Z = 49
Z = 49, A = 113 N = 64, This could be an isotope of indium
Z = 49 N = 61, A = 113 , this could also be an isotope of indium
A = 110, N = 49 it means Z = Z - N = 110-49 = 61 So this is not isotope of indium
