Which of the following gives propyne on hydrolysis?

In the molecule $CH_3-C \equiv C-CH=CH_2$,the maximum number of carbon atoms arranged linearly is

Identify the product $D$ in the following series of reaction: $CH_3COOH$ $\xrightarrow{LiAlH_4} A$ $\xrightarrow{H^{+}, 443 \ K} B$ $\xrightarrow{Br_2} C$ $\xrightarrow{alc. KOH} D$

Addition of $HCN$ to ethyne in the presence of $Ba(CN)_2$ as a catalyst gives:

$A$ compound is treated with $NaNH_2$ to give a sodium salt. Identify the compound.

Which is the most reactive hydrocarbon among the following?