Which one of the following reagents is used for the detection of unsaturation in alkenes?

For the following reactions,the major products are shown: $H_2C=CH-CH=CH_2$ $\xrightarrow[0^\circ C]{HBr} CH_2=CH-CH(Br)-CH_3$ $\xrightarrow{25^\circ C} Br-CH_2-CH=CH-CH_3$. These provide an example of $1$ control at low temperature and $2$ control at higher temperature.

Ethylene reacts with sulphur monochloride to form

The product obtained when $2-$methylpropan$-2-$ol is treated with alumina $(Al_2O_3)$ at $423 \ K$ is

The product obtained by the reaction of propene with $HBr$ in the presence of peroxide is......

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