The members of a family of an element that all have the same number of protons but different numbers of neutrons are called:

isotopes

The correct answer is option 1. isotopes.

The members of a family of an element that all have the same number of protons but different numbers of neutrons are called Isotopes.

Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. This results in variations in atomic mass among isotopes of the same element. Isotopes have similar chemical properties but may have different physical properties due to their differing atomic masses.