Which of the following gives propyne on hydrolysis?

The hydrocarbon which can react with sodium in liquid ammonia is

By heating a mixture of $CHCl_3$ with silver powder,the compound formed is

Given below are two statements:
Statement $I$: One mole of propyne reacts with excess of sodium to liberate half a mole of $H_2$ gas.
Statement $II$: Four $g$ of propyne reacts with $NaNH_2$ to liberate $NH_3$ gas which occupies $224 \ mL$ at $STP$.
In the light of the above statements,choose the most appropriate answer from the options given below:

The catalyst required for the dimerization of acetylene to form chloroprene is ....

Give a brief note on the acidic nature of alkynes.