All isotopes of a particular element have the same atomic number. how then do the isotopes of a particular element differ?
a. they have less or more protons.
b. they have less or more neutrons.
c. they have less or more electrons.

Option (b) is the correct answer.

Explanation:

Isotopes are the species that have same atomic number.

For example, and are isotopes. As both of them has 6 protons and there are 6 neutrons in . There are 7 neutrons in .

It is known that atomic number is the total number of present in an atom. Whereas mass number is the sum of total number of protons and neutrons present in an atom.

               Atomic mass = no. of protons + no. of neutrons

Therefore, we can conclude that when two elements are isotopes then the isotopes of a particular element differ as they have less or more neutrons.