Question

why is reaction between Methane and chlorine considered substitution reaction

Answer 1

When a mixture of methane and chlorine is exposed to ultraviolet light - typically sunlight - a substitution reaction occurs and the organic product is chloromethane. CH4 + Cl2 CH3Cl + HCl. However, the reaction doesn't stop there, and all the hydrogens in the methane can in turn be replaced by chlorine atoms. hope it help

Answer 2

Because in this reaction we remove the hydrogen by chlorine and form the product called ammonium chloride.

CH4+Cl gives CH3Cl