Select the correct statement(s) about the acidity of alkynes.

1. ABut-2-yne is more acidic than but-1-yne because it has more alkyl groups.
2. BSodium ethynide is protonated by water, regenerating ethyne.
3. CThe $\mathrm{sp}$ carbon has 50 percent s-character, which stabilises the conjugate base $\mathrm{R}-\mathrm{C}\equiv \mathrm{C}{}^{-}$.
4. DEthyne is converted quantitatively into sodium ethynide by aqueous $\mathrm{NaOH}$.