Question

Isotopes: are atoms of different elements which have the same mass are atoms of the same element with equal numbers of neutrons are atoms of the same element with different numbers of neutrons are atoms of the same element with equal numbers of protons and neutrons are atoms that have gained or lost electrons

Answer 1

I can't understand your option because there is no full stop however

isotopes are 2 or more form of elements that contain equal number of proton but different number of neutron in their nuclei

Answer 2

atoms of the same element with equal numbers of neutrons