Question

Oxidation state of phosphorus in pyrophosphoric acid is:

• A. 5
• B. 3
• C. 4
• D. 1

Answer 1

Answer: (A)

Pyrophosphoric acid is
$\stackrel{+1}{H_4}\stackrel{x}{P_2}\stackrel{-2}{O_7}$
$(+1\times 4)+2x+(-2\times 7)=0$
$+4+2x-14=0$
$2x=14-4$
$2x=10$
$x=+5$