Write the halogenation reaction of alkenes.

(N/A) $(i)$ Common reaction: In this reaction,the $\pi$-bond breaks,and halogen atoms are attached to the adjacent carbon atoms via $\sigma$-bonds.
$(ii)$ Type of reaction: When an alkene reacts with $X_2$ ($X = Cl$ or $Br$),a vicinal dihalide is formed. This is an electrophilic addition reaction. In this process,an unsaturated hydrocarbon is converted into a saturated dihalide. $A$ cyclic halonium ion intermediate is formed during the reaction.
$(iii)$ Alkenes react with chlorine $(Cl_2)$ and bromine $(Br_2)$ to give addition products,forming vicinal dihalides and vicinal dibromides,respectively.
Example $(a)$ Chlorination:
$CH_2=CH_2 + Cl_2 \rightarrow CH_2(Cl)-CH_2(Cl)$ ($1,2$-dichloroethane)
$CH_3-CH=CH_2 + Cl_2 \rightarrow CH_3-CH(Cl)-CH_2(Cl)$ ($1,2$-dichloropropane)
Example $(b)$ Bromination (Test for unsaturation):
$CH_2=CH_2 + Br_2 \xrightarrow{CCl_4} CH_2(Br)-CH_2(Br)$ ($1,2$-dibromoethane)
$CH_3-CH=CH_2 + Br_2 \xrightarrow{CCl_4} CH_3-CH(Br)-CH_2(Br)$ ($1,2$-dibromopropane)
General reaction:
$R_2C=CR_2 + X_2 \rightarrow R_2C(X)-CR_2(X)$ (Vicinal dihalide)