An alkene reacts with a strong protic acid to form a carbocation. however, an alkene will react with a halogen electrophile to form a cyclic intermediate. draw the curved arrow notation for both reactions.

Reaction mechanisms are shown below.

Explanation:

Alkene gives nucleophilic addition reaction with strong protic acid.

Proton from a strong protic acid ruptures pi-bond in alkene and makes a new C-H sigma bond and thereby produces a carbocation.

Lone pair on halogen atom first adds onto double bond by rupturing the pi-bond and this pi-bond electrons then simultaneously substitutes a halogen atom from diatomic molecule of halogen to produce a cyclic halogenium cation by forming two new C-X sigma bonds. (X=halogen atom)

Reaction mechanism has been shown below.

what are the choices?