Answer: D
Mg inserts into the weaker C-Br bond, giving 4-ClCX6HX4MgBr; the C-Cl bond stays. Addition to propanone gives 2-(4-chlorophenyl)propan-2-ol, a tertiary benzylic alcohol, which dehydrates with hot conc. HX2SOX4 to the alkene 4-ClCX6HX4−C(CHX3)=CHX2.