The correct option is A HC≡CH>H3C−C≡CH>H2C=CH2>H3C−CH3
Higher is the s character stronger the acid.
HC≡CH has 50% s-character, hence it has the most stable conjugate base meaning weak conjugate base. As we know weaker the conjugate base will be, stronger the acid. So HC≡CH is the most acidic.
H3C−C≡CH also has sp carbons, but there is a CH3 group attached to an sp carbon atom which will destabilise the conjugate base. Hence it is less acidic than HC≡CH.
H2C=CH2 and H3C−CH3 have sp2 and sp3 carbons respectively. Hence the acidic order of H2C=CH2 is greater than that of H3C−CH3.
So, the correct order of acidity will be:
HC≡CH>H3C−C≡CH>H2C=CH2>H3C−CH3