Which is represented by the formula $C_n H_{2n - 2}$?

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:

What is formed when acetylene reacts with alkaline $KMnO_4$?

Which of the following does not react with acetylene?

Which of the following alkynes,upon treatment with $H_2$ $(2 \ mole)$ / $Pt$,gives an optically inactive compound?

Hydration of propyne results in the formation of.......