The major products A and B formed in the following reactions are

Concept:

Reactivity difference of the both the reagents will lead to formation of different products.

Reagent I is having terminal epoxide ring with secondary alkyl chloride group. Chlorine is poor leaving group than bromine and moreover it is present on secondary position, thus it can not attack directly.

Reagent II is having halide group i.e., Bromine on terminal position and is good leaving group both of these point making it more reactive reagent than I.

Role of HgCl₂ is depotection of Dithiane ring by S_N² mechanism.

Mechanism:

→ Reaction with reagent I:

→ Reaction with reagent II:

Conclusion:-

So, The major products A and B formed in the following reactions are option 1