Product $(A)$ is

Identify product $B$ in the following reaction sequence:
$(CH_3)_2C=C(CH_3)_2$ $\xrightarrow{X_2, H_2O} A$ $\xrightarrow{OH^{-}} B$

Match the chemical conversions in List-$I$ with the appropriate reagents in List-$II$ and select the correct answer using the code given below the lists:
List-$I$:
$P$. $tert$-butyl chloride $\rightarrow$ isobutylene
$Q$. Sodium $tert$-butoxide $\rightarrow$ $tert$-butyl ethyl ether
$R$. $1$-methylcyclopentene $\rightarrow$ $1$-methylcyclopentanol
$S$. $1$-methylcyclopentene $\rightarrow$ $2$-methylcyclopentanol (trans-isomer)
List-$II$:
$1$. $(i) \ Hg(OAc)_2; (ii) \ NaBH_4$
$2$. $NaOEt$
$3$. $EtBr$
$4$. $(i) \ BH_3; (ii) \ H_2O_2/NaOH$
Codes: $P \quad Q \quad R \quad S$

The major product in the following reaction sequence is:

Consider the following two reactions $A$ and $B$.
Numerical value of [molar mass of $x$ + molar mass of $y$] is . . . . . . .

$A, B, C, D$ in the following reactions are