What is the major product expected from the following reaction?

Which one of the following is an electrophilic addition reaction?

In polyenes that contain differently substituted $(C=C)$ double bonds,it is possible to hydrogenate chemoselectively one $(C=C)$ double bond. The product of the reaction of limonene with one mole of $H_2$ in the presence of $PtO_2$ is:

What is the major product of the following reaction?
$CH_2=CH-CH=CH_2 + Br_2 \text{ (1 eq)} \xrightarrow{\Delta} ?$

Identify $X$ in the following reaction sequence: Cyclopentane $\xrightarrow{Cl_2/hv} A$ $\xrightarrow{alc. KOH} B$ $\xrightarrow{O_3, Zn/H_2O} X$

Addition of $HCl$ to $3,3$-dimethyl-$1$-butene yields two products,one of which has a rearranged carbon skeleton. Among the following carbocations,select the possible intermediates in that reaction:
$1.$ $(CH_3)_3C-C^+H-CH_3$
$2.$ $(CH_3)_3C-CH_2-C^+H_2$
$3.$ $(CH_3)_2C(Cl)-C^+(CH_3)_2$
$4.$ $(CH_3)_2C^+-CH(CH_3)_2$