Question

The oxidation state of phosphorus in pyrophosphorus acid is

• A. +3
• B. +1
• C. +4
• D. +5

Hint:

For oxidation state calculations, always write the molecular formula clearly and assign standard oxidation states to hydrogen and oxygen before solving for the unknown element.

Answer 1

The Correct Option is A

Step 1: Write the molecular formula of pyrophosphorous acid.
Pyrophosphorous acid has the molecular formula: \[ \mathrm{H_4P_2O_5} \]
Step 2: Assign oxidation states to known elements.
Hydrogen usually has an oxidation state of \(+1\).
Oxygen usually has an oxidation state of \(-2\).
Step 3: Let the oxidation state of phosphorus be \(x\).
There are 2 phosphorus atoms, so total oxidation state contribution is \(2x\).
Step 4: Apply the oxidation state rule for a neutral molecule.
Sum of oxidation states = 0
\[ 4(+1) + 2x + 5(-2) = 0 \]
Step 5: Solve the equation.
\[ 4 + 2x - 10 = 0 \]
\[ 2x - 6 = 0 \]
\[ 2x = 6 \]
\[ x = +3 \]
Step 6: Conclusion.
The oxidation state of phosphorus in pyrophosphorous acid is \(+3\).