Given below are two statements. One is labelled as Assertion (A) and the other is labelled as reason (R). 

 

Ethyne> Ethene >Ethane .

This can be explained with the Hydrogen donating tendency of hydrocarbon, carbon which is more electronegative will create high positive charge on hydrogen, hence that hydrocarbon will me most acidic.

Ethyne is most acidic because it contains acidic hydrogen (hydrogen connected with sp hybridized carbon ) % S character is 50%,hence most electronegative .

Both the hydrogen atoms are identical and connected with carbon which is sp hybridised hence, Ethyne is most acidic.

Ethene is less acidic than Ethene as the carbon containing hydrogen is sp2 hybridized (%s character is 33.3, hence less electronegative).

Four identical hydrogen connected with sp² hybridised carbon,hence less acidic in nature.

Ethane is least acidic because both the carbons are sp³ hybridised (%s character is 25%, hence least electronegative).

Six hydrogen is attached with sp³ hybridised carbon.