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.