Given are $\mathrm{H}_3 \mathrm{PO}_2, \mathrm{H}_3 \mathrm{PO}_3, \mathrm{H}_3 \mathrm{PO}_4$ and $\mathrm{H}_4 \mathrm{P}_2 \mathrm{O}_7$. Which of the above oxacids results into two series of salts?

• A

  $\mathrm{H}_3 \mathrm{PO}_2$
• Correct answer
  B

  $\mathrm{H}_3 \mathrm{PO}_3$
• C

  $\mathrm{H}_3 \mathrm{PO}_4$
• D

  $\mathrm{H}_4 \mathrm{P}_2 \mathrm{O}_7$

Solution

Phosphorus acid $\left(\mathrm{H}_3 \mathrm{PO}_3\right)$ is a diprotic acid. If forms two series of salts such as $\mathrm{NaH}_2 \mathrm{PO}_3$ and $\mathrm{Na}_2 \mathrm{HPO}_3$ but none of the type $\mathrm{NaPO}_3$ with $\mathrm{NaOH}$. Its structure is as

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