Chemistry - Atomic Structure Question with Solution | TestHub

An isotope refers to atoms of the same element that have the same number of protons but different numbers of neutrons. This means they have the same atomic number but different mass numbers.

Option B, ${\mathrm{O}}^{16}$ and ${\mathrm{O}}^{18}$, represents two isotopes of oxygen. Both have 8 protons, but ${\mathrm{O}}^{16}$ has 8 neutrons, while ${\mathrm{O}}^{18}$ has 10 neutrons.