Where can isotopes be found?

Isotopes can be found in any element.

A definitive statement on an isotope is ' An Atom has a different number of neutrons'.

The element that exhibits in large proportion two isotopes is chlorine.

There is Chlorine-35 & Chlorine-37

The numbers being the atomic masses of of chlorine. The difference of '2' ( 37-35) is made up by a different number of neutrons.

Chlorine-35 ; 17 protons, 18 neutrons and 17 electrons

Chlorine-37 ; 17 protons. 20 neutrons and 17 electrons.

The Atomic Mass of Chlorine is given as 35.5 . This because there are 75% of Cl-35 atoms and 25% of Cl-37 atoms.

NB Not all isotopes are Radio-Active, but some are!!!!!