Question

an isotope is a version of an element with the same number of protons but different number of _____________. neutron electron

Explanation:

Isotopes are defined as atoms of the same element (same number of protons) that have different numbers of neutrons. Electrons are not involved in the definition of isotopes as they can be lost or gained in chemical reactions (forming ions), while isotopes specifically refer to variations in neutron count.

Answer:

neutron