Question

Isotopes of the same element differ in their ____.

number of electrons
number of protons
atomic number
mass number

Answer 1

He is correct

Step-by-step explanation:

Just took my lesson and got 100% the answer is mass

Answer 2

Isotopes of the same elements differ in their mass number. Isotopes are those elements have the same protons but differs from their neutrons. That is why it differs in their mass number because the mass number is the sum of protons and neutrons.