Explain the given reactions with the examples.
(a) Hydrogenation reaction , (b) Oxidation reaction
(c ) Substitution reaction , (d) Saponification reaction
(e) Combustion reaction

Explanation

(a) Hydrogenation reaction The addition of hydrogen to the unsaturated molecule to make it saturated is known as hydrogenation.
e.g., `underset("Ethene")(CH_(2)=CH_(2))+H_(2)underset(Ni)overset(200^(@)C)tounderset("Ethane")(CH_(3)-CH_(3))`.
(b) Oxidation reaction The reactions in which an oxidising agent supply nascent oxygen for oxidation are called oxidation reactions.
e.g., `CH_(3)CH_(2)OHunderset(K_(2)Cr_(2)O_(7))overset([0])toCH_(3)CHOunderset(K_(2)Cr_(2)O_(7))overset([0])toCH_(3)COOH` (c ) Substitution reaction When one atom or a group of atoms replaces or substitutes another atoms or a group of atoms from the molecule, it is known as substitution reaction
e.g., `CH_(4)+Cl_(2)overset("Sunlight")toCH_(3)Cl+HCl`
(d) Saponification reaction When esters are hydrolysed in the presence of a base (NaOH) then the reaction is called saponification reaction.
e.g., `CH_(3)COOCH_(3)+NaOHtoCH_(3)COONa+CH_(3)OH`
(e) Combustion reaction Organic compounds burn readily in air to form `CO_(2)` and water vapour along with lot of heat. This is known as combustion reaction.
`C_(2)H_(5)OH+3O_(2)to2CO_(2)+3H_(2)O+"Energy"`