Answer:
C. Neutrons
Explanation:
Elements principal differentiation is their number in protons, this means that an atom with a different number of protons is NOT an isotope is a completely different element, for example, hydrogen and helium have a proton of difference (1 for H, 2 for He).
Positrons, electrons, and ions just change the charge in an element, this doesn't affect its mass, therefore, they are no isotopes.
By definition, an isotope is a variant of a particular chemical element that differs in neutron number (meaning isotopes have different masses) but has the same number of protons and electrons. Isotopes are represented with a superscript number to the left of the element, for example, for hydrogen, deuterium [tex]^{2}H[/tex] indicates one neutron and one proton.
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