Question

How do atoms of an element exist in nature?

Answer 1

Atoms of most of the elements exist in the form of molecule or ion, since they are more reactive.For ex:- Hydroden, Oxygen, etc.However, atoms of some elements, which are non-reactive, exist in free-state in nature.

Answer 2

Some atoms of an element occur independently in nature. For example, Helium (He), Neon (Ne), etc. They are called monoatomic elements. 
         However, atoms of many elements cannot exist independently in nature. They form molecules containing two or more atoms. For example, the molecules of hydrogen, nitrogen, oxygen and chlorine have two atoms each. They are known as diatomic elements. Thus, $H_{2}$ represents a molecule of hydrogen, $O_{2}$ a molecule of oxygen, $N_{2}$ a molecule of nitrogen and $Cl_{2}$ a molecule of chlorine. 

Hope this may help you.