An alkyiic shows acidic nature only if it contains terminal hydrogen atom. This can be explained by considering the Sp hybrid orbitais of carbon atom in alkynes. The percentage of s-character of sp hybrid orbital (50%) is more than sp2 hybrid orbital ofalkenes (33%) and sp3 hybrid orbital of alkanes (25%). Because of this, carbon atom becomes more electronegative, thus facilitating donation of H ions to bases. So hydrogen attached to triply bonded carbon atoms is acidic in nature.
