Alkanes have single bond, but why are they less reactive as compared to alkenes or alkynes which have respectively double or triple bonds ?

Dear Vasudev,
alkanes have only one sigma bond which makes them stable and allows delocalisation of electrons and hence hyperconjugation,
but alkenes and alkynes have one or two additional pie bonds which restricts the above mentioned phenomena.
as a result they tend to break their pie bond in order to achieve a single sigma bond and a stable structure that may allow resonance.
Regards.

pi bond is easily brekable than sigma bond so they are more reactive

sorry actually a little misconcept in my ans.
actually the pi bonds in alkenes and alkynes prevent rotation of the carbon atom...
but in case of alkane it is possible due to the presence of sigma bond which allows rotaion.
as a result the alkenes and alkynes try to break their pi bonds in order to achieve a single sigma bond for free rotation.

this is soo as alkanes only  have one sigma bond which is quite strong as compared to a pi bond present in alkenes,

hence alkenes are much more reactive than alkanes..