Question

Find the oxidation state of Phosphorus in \( H_3PO_4 \) and \( H_3PO_3 \).

• A. \(+5\) and \(+3\)
• B. \(+3\) and \(+5\)
• C. \(+4\) and \(+3\)
• D. \(+5\) and \(+4\)

Hint:

Always assign known oxidation states first (H = +1, O = -2), then solve for the unknown element.

Answer 1

The Correct Option is A

Concept: The oxidation state of an element is calculated by assuming:

• Hydrogen = \(+1\)
• Oxygen = \(-2\)
• Sum of oxidation states in a neutral compound = \(0\)

Step 1: {Find oxidation state of P in \(H_3PO_4\).} Let oxidation state of phosphorus = \(x\) \[ 3(+1) + x + 4(-2) = 0 \] \[ 3 + x - 8 = 0 \] \[ x -5 = 0 \] \[ x = +5 \]
Step 2: {Find oxidation state of P in \(H_3PO_3\).} Let oxidation state of phosphorus = \(x\) \[ 3(+1) + x + 3(-2) = 0 \] \[ 3 + x - 6 = 0 \] \[ x -3 = 0 \] \[ x = +3 \]
Step 3: {Conclusion.} \[ H_3PO_4 : +5 \] \[ H_3PO_3 : +3 \]