The reagent ' X ' used in the following reaction to obtain good yield of the product is

• A

  $\mathrm{KI}, \mathrm{H}_2 \mathrm{SO}_4$
• Correct answer
  B

  $\mathrm{KI}, 95 \% \mathrm{H}_3 \mathrm{PO}_4$
• C

  $\mathrm{NaI}, \mathrm{ZnCl}_2$
• D

  $HI$

Solution

$\mathrm{H}_3 \mathrm{PO}_4+3 \mathrm{KI} \rightarrow 3 \mathrm{HI}+\mathrm{K}_3 \mathrm{PO}_4$

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