If two atoms are isotopes of the same element, they have the same number of but will have different numbers of a: protons; neutrons b: neutrons; electrons c: neutrons; protons

A.

Explanation:

if it's the same element the protons will always be the same, but have different neutrons, and neutrons is made up of protons and atomic mass, which atomic mass numbers can be calculated different where in return gives different numbers of neutrons.

EX: say the element is carbon, carbon has 6 protons and that won't change, but carbon can have an atomic mass of 12, 13, or 14, etc. so when you make up the neutrons you add protons and atomic mass, 6 + 12 = 18 N

6 + 13 = 19 N

6 + 14 = 20 N

it's c. elements are placed in rows based on how may valencies electrons have.