The number(s) of -OH group(s) present in $\mathrm{H}_3 \mathrm{PO}_3$ and $\mathrm{H}_3 \mathrm{PO}_4$ is/are

• A

  3 and 3 respectively
• B

  3 and 4 respectively
• Correct answer
  C

  2 and 3 respectively
• D

  1 and 3 respectively

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