The hydrogen atoms attached to the triple bond of the alkynes, i.e., acetylenic hydrogens are acidic in nature and known as active hydrogen. This acidic property is shown by terminal alkynes or 1-alkynes only (alkynes in which the triple bond is at the end of the chain). The reaction with Na in liquid NH3 is considered as test of acidity of terminal alkynes. The reason of acidity of terminal alkynes is greater electronegativity of carbon atom of C−H triple bond, which is sp-hybridised. In other words, electrons of C−H bond are displaced more towards the carbon atom than towards the hydrogen atom, hence it can be removed as a proton (H+)by a strong base. Consequently, alkynes behave as acids.