Why are certain compounds called hydrocarbons? Write the general formula for homologous series of alkenes and alkynes and also draw the structure of the first member of each series. Write the name of the reaction that converts alkenes into alkanes and also write a chemical equation to show the necessary conditions for the reaction to occur.

Explanation

Hydrocarbons. As these compounds have only atoms of carbon and hydrogen elements in their molecules, so these are called Hydrocarbons.
General formulae:
Alkanes `C_(n) H_(2n+2)`
Alkenes `C_(n)H_(2n)`
Alkynes `C_(n)H_(2n-2)`
Structures of first member of each:

The reaction which convert Alkenes into Alkanes is called Addition Reaction.
`underset("(Ethene)")(H_(2)C=CH_(2)+H_(2)) underset("Heat")overset(Ni) (to) H_(3)Cunderset("Ethane")underset("")(-CH_(3))`
Ni (Nickel) metal acts as catalyst in this reaction.