Question

The oxidation number of phosphorus in pyrophosphoric acid is

• A. +3
• B. +1
• C. +4
• D. +5

Answer 1

Answer: (D)

+5

Answer 2

Pyrophosphoric acid ${H_4P_2O_7}$
Let oxidation state of phosphorus is x
$(4 \times 1 + (- 2) \times 7 + 2 x) = 0$
$\therefore$ 2x = 10 or x = +5