Alkynes are weakly acidic.
Compared to alkynes, alkenes are still weak in acidic behaviour. Practically they do not shown any acidic behaviour.
The acidic property is because of s character.
Alkynes are sp hybridized. (50% s character)
Alkenes are sp² hybridized (33% s character)
Because of lesser s character, these carbon atoms are much less electronegative than the carbon atoms taking part in the triple bond.
Therefore, the release of H+ ion from an alkene molecule is difficult and they do not show acidic character.
In term of Ka
Alkynes have 10^-26 and
alkenes have 10^-36.