Among $HCl$,$HBr$,and $HI$,which reactant gives the Kharasch effect (peroxide effect) with an alkene?

The reaction of $4$-methyloct$-1-$ene $(P, 2.52 \ g)$ with $HBr$ in the presence of $(C_6H_5CO_2)_2O_2$ gives two isomeric bromides in a $9:1$ ratio,with a combined yield of $50 \%$. Of these,the entire amount of the primary alkyl bromide was reacted with an appropriate amount of diethylamine followed by treatment with aqueous $K_2CO_3$ to give a non-ionic product $S$ in $100 \% $ yield. The mass (in $mg$) of $S$ obtained is. . . . . . . [Use molar mass (in $g \ mol^{-1}$) : $H=1, C=12, N=14, Br=80$]

The metal used for the de-bromination reaction of $1, 2$-dibromoethane is:

In the given reaction
$CH_3CH_2CH=CHCH_3$ $\xrightarrow{X}$ $CH_3CH_2COOH + CH_3COOH$
The $X$ is

$CH_3-CH(CH_3)-CH=CH_2 + HBr \rightarrow A$. $A$ (predominantly) is:

The major products $P$ and $Q$ from the below reactions are :
$CH_3CH=CH_2 \xrightarrow{HBr} P$
$CH_3CH=CH_2 \xrightarrow[(BH_3)_2]{H_2O, H_2O_2 / OH^-} Q$