a
The formation of \(C - H\) bond in acetylene involves \(sp\)-hybridised carbon atom. Since \(s\)-electrons are closer to the nucleus than \(p\) electrons, \(sp\) hybrid orbitals are more electronegative through its smaller(in length) and thicker lobes which increases the time spent by electrons near nucleus than in \(sp ^2\) and \(sp ^3\). Thus, the electrons present in a bond having more \(s\)-character will be more closer to the nucleus. In alkynes ( \(\equiv C - H )\) bond, \(s\)- 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 \(sp ^2, sp ^3\) and hence the hydrogen atom present on carbon atom \((\equiv C - H )\) can be easily removed.