The correct option is D substitution reaction
A substitution reaction is a chemical reaction during which one atom or group of atoms in a chemical compound is replaced by another atom or group of atoms.
Chlorination of methane is a substitution reaction because chlorine atom replaces hydrogen atom from the methane molecule. The reaction occurs as follows:
CH4(g)+Cl2 (g)sunlight−−−−→CH3Cl (g)+HCl (g)Methane Chlorine Chloro Hydrogen methane chloride