Question

Write the name and general formula of a chain of hydrocarbons in which an addition reaction with hydrogen can take place. Stating the essential conditions required for an addition reaction to occur, write the chemical equation giving the name of the reactant and the product of such a reaction.

Answer 1

unsaturated hydrocarbons such as alkenes and alkynes give addition reaction and hydrogenation reaction
alkenes general formula = CₓH₂ₓ
alkyens general formula = CₓH₂ₓ₋₂
( note: there may be hydrocarbon present which may have same general formula but no double bond but instead a ring, those compounds will not give addition reaction)
the necessary condition to show hydrogenation reaction and addition reaction is that unsaturation is present due to the presence of double or triple bond and not only due to the presence of ring
eg of addition reaction 
ethene when treated with Br₂ in presence of CCl₄ it yields 1,2-dibromoethane