Question

Arrange ethyne,ethane and ethene in the order of increasing acidity .

Answer 1

With increase in s character acidity increases.
Ethyne (H-C≡C-H): here carbon is sp hybridised : % s character = 50 %
Ethene (H2C=CH2): here carbon is sp2hybridised : % s character = 33.3 %
Ethane (H3C-CH3): here carbon is sp3hybridised : % s character = 25 %
 
As order % s character is ethane< ethene < ethyne, so the order of acidity is ethane< ethene < ethyne.

Answer 2

ethane , ethene ,ethyne.