Which hydrocarbon reacts with sodium in liquid ammonia?

Which of the following compounds is capable of reacting with ammoniacal $AgNO_3$ solution?

When propyne is treated with dilute $H_2SO_4$ and $HgSO_4$,the major product is

The bond length between the hybridized carbon atom and another carbon atom is minimum in:

The product $(C)$ of the above reaction is:
Maleic anhydride $\xrightarrow{H_3O^+}$ $(A)$ $\xrightarrow{NaOH}$ $(B)$ $\xrightarrow{\text{Kolbe electrolysis}}$ $(C)$

Cyclo$[18]$ carbon is an allotrope of carbon with molecular formula $C_{18}$. It is a ring of $18$ carbon atoms, connected by alternating single and triple bonds. The total number of triple bonds present in this cyclocarbon is: