No, Prasenjeet, we cannot lump alkanes, alkynes and alkenes into one "homologous" series.
The general formula for an alkane is C_{n}H_{2n + 2} (n ≥ 1) in which the repeating unit is CH_{2}
For 1alkenes the general formula is C_{n}H_{2n} (n ≥ 2) for which the repeating unit is also CH_{2}, but notice how the general formula differs from that of alkanes.
As a final example consider 1alkynes for which the general formula is C_{n}H_{2n} − 2 (n ≥ 2).
Compounds form a homologous series as long as they have the same general formula. Thus methane, ethane, propane, butane etc. form one homologous series (the alkanes). Alkenes and alkynes form their own series.
Jan 20

William S.