How are two samples of an element referred to when they possess differing numbers of neutrons?

A) As isotopes
B) As allotropes
C) As ions
D) None of the above. They are different elements if the samples have differing numbers of neutrons.

Isotopes

Forms of the same chemical element that have different numbers of neutrons, leading to variations in their total number of nucleons.

Neutrons

Subatomic particles found in the nucleus of an atom, carrying no electric charge and having a mass slightly larger than that of a proton.

Allotropes

Different forms of the same element in the same physical state with different structures and properties.