The formation of C−H bond in acetylene involves sp -hybridised carbon atom. since s-electrons are closer to the nucleus than p -electrons, the electrons present in a bond having more s -character will be more closer to the nucleus. In alkynes s character is 50% the electrons constituting this bond are more strongly bonded by the carbon nucleus. Thus, acetylenic C-atom becomes more electronegative in comparison to sp2,sp3 and hence the hydrogen atom present on carbon atom (≡C−H) can be easily removed.