The molecule having an atomicity of 4 is :

Atomicity: The number of atoms constituting a molecule is known as its atomicity.

Sulphur molecule (S₈) : Atomicity is 8

Ozone molecule (O₃): Atomicity is 3

Phosphorus molecule (P₄): Atomicity is 4

Methane molecule (CH₄): Atomicity is 5

Thus, option C is correct.