An isotope of an element is formed
i.by adding protons to, or removing protons from, the atom.II.by adding neutrons to, or removing neutrons from, the atom.III.by adding electrons to, or removing electrons from, the atom.

Question

Quizplus · Accepted Answer

Isotopes are formed by adding or removing neutrons from the atom, which changes the atomic mass but not the atomic number (since protons determine the element). Adding or removing protons would result in a different element altogether, while adding or removing electrons would result in an ion of the same element but not a different isotope.

An Isotope of an Element Is Formed