Alkynes having sp -hybridised carbon has max. s character and hence max. electronegativity with the result it attracts the electron pair of the bond C−H to a greater extent and makes the removal of proton easier than the alkenes having sp2 hybridised carbon. Now presence of electron donating group (−CH3) in alkyne CH3−C≡CH decreases acidic strength of the compound. Hence the correct order of acidic strength is HC≡CH>H3C→C≡CH>CH2=CH2