The reagent required for the following two step transformation are

• A

  (i) HBr, benzoyl peroxide ; (ii) $\mathrm{CH}_{3} \mathrm{CN}$
• Correct answer
  B

  (i) $\mathrm{HBr}$, (ii) $\mathrm{NaCN}$
• C

  (i) $\mathrm{Br}_{2}$, (ii) $\mathrm{NaCN}$
• D

  (i) $\mathrm{NaBr}$, (ii) $\mathrm{NaCN}$

Hence, the correct answer is option: 'B'.