Why are 16O and 18O isotopes of each other?

[Billtcm]

Hi on a test there was a question that said "Which symbols represent atoms that are isotopes of each other?" the answer turned out to be 16O and 18O, the numbers referring to the number of protons and neutrons. Anyhow I wanted to know what you have to do in order to get that answer as I got this question wrong. Thank you

 

[Pyrrhus]

Probably has to do with the definition of an isopote. They are atoms of the same element with the same aotmic number, but different atomic mass. Do you know what the atomic number represents? then you probably know the particle incrementing its mass.

 

[James R]

Isotopes are atoms with the same number of protons but different numbers of neutrons. For example, two isotopes of Oxygen are $^{16}_8O$ and $^{18}_8O$. The first has 8 protons and 8 neutrons; the second has 8 protons and 10 neutrons. The number at the bottom is the atomic number (number of protons). The number at the top is the mass number (number of protons plus neutrons).