Hi Candidate,

Substitution reaction is the reaction in which a leaving group gets substituted by the attack of a nucleophile. Substitution reaction is of two types- SN 1 and SN 2. Example of substitution reaction is-  methyl bromide reacts with (-OH) to form methanol.

Elimination reaction refers to a reaction in which two substituents are removed through a one step or two step mechanism. Example of Elimination reaction is- ethanol upon dehydration gives ethene + water.