Why do alkenes and alkynes undergo addition reactions ? Describe some important addition reactions of alkenes and alkynes.

Explanation

A carbon-carbon double bond is made up of sigma and a pi bond.
This is formed by the sideways overlap of p-orbitals.
The overlapping of orbitals here is much lesser extent as compared to the sigma bond.
Thus , energy of sigma bond is more compared to the energy of a pi bond. The electron density in a pi bond is diffused and more exposed to the ready attack of an electrophile.
Due to these factors, C= C bond in an alkene, is under a sort of strain and pi bonds convert themselves to 2 sigma bonds.
Hence, alkenes invite electrophiles to attack on them and undergo electrophilic addition reactions.