Ascending acidity order of the following H atom is:

Step 1: Acidic Strength and Hybridization Acidic strength increases with the $s$-character of the hybridized carbon atom.

• $\ce{CH \equiv CH}$ ($sp$ carbon, 50% $s$-character)
• $\ce{CH2 = CH2}$ ($sp^2$ carbon, 33% $s$-character)
• $\ce{CH3 - CH3}$ ($sp^3$ carbon, 25% $s$-character)

Step 2: Conclusion Since an $sp$ carbon is most electronegative, it holds the negative charge in the conjugate base most effectively. Thus, order is: $\ce{CH \equiv CH > CH2 = CH2 > CH3 - CH3}$.

$\boxed{\text{Answer: (a)}}$