Question

What do two different neutral isotopes of the same element have in common?

Answer 1

Answer:

Same number of protons.

Explanation:

Isotopes is defined as the atoms of same element which are exist in different forms.

The posses the same number of proton but different number of neutrons. Different isotopes of same elements posses different masses. Different isotopes of the same elements posses same atomic number.

The atomic number is decided  by the number of protons and atomic masses are different for these isotopes which suggest different number of neutrons.

Answer 2

Since they're the same element, they will have the same number of protons (and, since they're neutral here, the same number of electrons as well). Changes in number of neutrons change the isotope of the element without changing the element itself.