The triple bond in ethyne $(C_2H_2)$ is formed from:

$CH_3-C \equiv CH \xrightarrow[(ii) H_2O_2/OH^{\Theta}]{(i) BH_3-THF} (P)$
$CH_3-C \equiv CH \xrightarrow[(ii) NaBH_4]{(i) Hg(OAc)_2/H_2O} (Q)$
Choose the correct option

What product is obtained by the oxymercuration of $1$-butyne using $HgSO_4 + H_2SO_4$?

$C_3H_4 + H_2O \xrightarrow[333 \ K]{Hg^{2+} / H^{+}} [X] \rightleftharpoons{\text{Tautomerisation}} Y$
$X$ and $Y$ are respectively

The reaction $Ph-C \equiv CH \xrightarrow[{(2)\,H_2O_2/OH^{-}}]{{(1)\,BH_3.THF}}$ Product; the product is

$CH_3-CH_2-CH_2-C\equiv CH + LiNH_2 \to (A) \xrightarrow{(CH_3)_2SO_4} (B)$
Give the structural formula of compound $(B)$.