Write the name and general formula of a chain of hydrocarbons in which an addition reaction with hydrogen is possible. State the essential condition for an addition reaction. Stating this condition,write a chemical equation giving the name of the reactant and the product of the reaction.

(A) The hydrocarbons in which an addition reaction with hydrogen is possible are known as $Alkene$s. Their general formula is $C_nH_{2n}$.
The essential condition for an addition reaction is the presence of a multiple bond (double or triple bond) between carbon atoms and the use of a catalyst such as $Ni$,$Pd$,or $Pt$.
Chemical equation (Hydrogenation of Ethene):
$CH_2=CH_2 + H_2 \xrightarrow{Ni/Pd/Pt} CH_3-CH_3$
Reactant: $Ethene$
Product: $Ethane$