Question

Why hydrogen atoms can be liberated as protons in ethyne?

Answer 1

In ethyne carbon atom is sp hybridised, having 50% s-character. Higher the s-character higher is the electronegativity of the carbon atom.
So shared pair of electrons is pulled towards carbon atom, creating partial positive charge on hydrogen atom, and making the C—H bond weak.
This is why ethyne can liberate H+ ions (protons) easily and show acidic character.

Answer 2

Answer:

The hydrogen atoms bonded with the terminal sp hydbridised carbon atoms can be easily liberated as protons leaving behind their corresponding conjugate base which is very stable since due to high s character (50%) In sp hydbridised carbon atom it's electronegativity is high and so the negative charge on that atom is stable even though the charge density does not get dispersed inspite of no scope of what we call as resonance.

So, yep In ethyne molecule the hydrogen atoms connected to either of the two terminal carbon atoms of this alkyne can be liberated as protons !

Hope this helps you ! ｡◕‿◕｡