Elements which have same number of protons but different number of neutrons are called as _________ ?

A. Isotopes
B. Isomers
C. Allotropes
D. Allomers

Atoms which have the same number of protons but different numbers of neutrons in the nucleus are known as isotopes. Because of the difference in the number of neutrons, they will have the same atomic number, but varying atomic mass (or mass number).