Question

Which of the following oxoacids of phosphorous has reducing character?

• A. H$_{6}$P$_{4}$O$_{13}$
• B. H$_{4}$P$_{2}$O$_{7}$
• C. H$_{3}$PO$_{3}$
• D. H$_{3}$PO$_{4}$

Answer 1

Answer: (C)

H$_{3}$PO$_{3}$

Answer 2

The reducing character of oxoacids of phosphorus is attributed to the presence of P-H bonds. These P-H bonds are not ionizable but can be oxidized, thus making the compound a reducing agent. H$_{3}$PO$_{3}$ (Phosphorous acid or Phosphonic acid) has one P=O bond, two P-OH bonds, and one P-H bond. The presence of the P-H bond imparts reducing character to H$_{3}$PO$_{3}$.