For making distinction between 2-pentanone and 3-pentanone the reagent to be employed is

• A

  $\mathrm{K}_2 \mathrm{Cr}_2 \mathrm{O}_7 \mathrm{H}_2 \mathrm{SO}_4$
• B

  $\mathrm{Zn}-\mathrm{Hg} / \mathrm{HCl}$
• C

  $\mathrm{SeO}_2$
• Correct answer
  D

  None of the above

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