What is meant by atomicity? How many different types of molecules are known on the basis of atomicity?

(N/A) The number of atoms present in one molecule of a substance is called its atomicity.
Depending on the number of atoms present in a molecule,the following types of molecules are known:
$(i)$ Monoatomic molecules: These consist of a single atom. Noble gases like $He$,$Ne$,and $Ar$ exist as monoatomic molecules.
$(ii)$ Diatomic molecules: These consist of two atoms,e.g.,$O_{2}$,$N_{2}$,$Cl_{2}$,$H_{2}$,$Br_{2}$,and $I_{2}$.
$(iii)$ Triatomic molecules: These consist of three atoms,e.g.,$O_{3}$ (Ozone molecule).
$(iv)$ Tetratomic molecules: These consist of four atoms,e.g.,$P_{4}$ (Phosphorus molecule).
$(v)$ Polyatomic molecules: These consist of more than four atoms,e.g.,$S_{8}$ (Sulphur molecule).
Note: All the above types represent molecules of an element,where atoms of the same element exist together as a single species in a free state.