Explain the following reactions with one example for each giving relevant chemical equations : (i) Hydrogenation reaction,
(ii) Oxidation reaction,
(iii) Substitution reaction,
(iv) Saponification reaction.

Explanation

(i) Hydrogenation reaction It is the process in which unsaturated compound reacts with hydrogen in presence of nickel as a catalyst to form saturated compound.

(ii) Oxidation reaction : When there is an addition of oxygen in the reaction, it is known as oxidation reaction.
`CH_(3)underset"Ethanol"(CH_(2)OH)+[O]overset"Alkalana"underset"KMnO"rightarrow underset"Ethanoic acid"(CH_(3)COOH +H_(2)O)`
(iii) Substitution reaction. Those reactions in which an atom or group of atoms of compound are replaced by other atom or group of atoms are called substitution reactions.
`underset"Mathane"(CH_(4)(g))+underset"Chlorine"(CI_(2)(g))+[O]overset"sunlight"rightarrow underset"Chloromethane"(CH_(3)CI(g)) + HCI(g)" Hydrogen chloride"`
(iv) Saponification reaction: lt is the reaction in which an ester reacts with sodium hydroxide to form sodium salts of acid and alcohol.
`underset"Ethyl ethanote"(CH_(3)COOC_(2)H_(5))+underset"Sodium ethanoate"underset(CH_(3)COONa+)underset"Sodium hydroxide"(NaOH)underset"Ethanola"underset(C_(2)H_(5)OH)rightarrow`