An oxoacid of phosphorus ' X ' reduces silver nitrate solution to metallic silver and gets oxidised to another compound $\mathrm{Y}. \mathrm{X}$ and Y respectively are.

• A

  $\mathrm{HPO}_3, \mathrm{H}_3 \mathrm{PO}_4$
• Correct answer
  B

  $\mathrm{H}_3 \mathrm{PO}_2, \mathrm{H}_3 \mathrm{PO}_4$
• C

  $\mathrm{H}_3 \mathrm{PO}_3, \mathrm{H}_3 \mathrm{PO}_2$
• D

  $\mathrm{H}_3 \mathrm{PO}_2, \mathrm{HNO}_3$

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