How will you prove that terminal hydrogen of alkynes is acidic?

(i) When sodium or potassium metal dissolved in liquid ammonia, reacts with 1-alkyne, giving corresponding sodium or potassium alkynides.

(ii) When acetylene is passed through an am- monical solution of cuprous chloride, then a red precipitate of copper acetylide is obtained.

These reactions prove that hydrogen atom at the terminal position in alkynes is acidic.