Question

What is the oxidation state of oxygen in peroxides?

• A. \( -2 \)
• B. \( -1 \)
• C. \( 0 \)
• D. \( +1 \)

Hint:

Remember the key exception: Oxygen usually has oxidation state \( -2 \), but in \textbf{peroxides} (because of the O–O bond) it becomes \( -1 \).

Answer 1

The Correct Option is B

Concept: The oxidation state represents the hypothetical charge assigned to an atom in a compound assuming complete transfer of electrons. For oxygen, the common oxidation states are:

• \( -2 \) in most oxides (e.g., \(H_2O\))
• \( -1 \) in peroxides (e.g., \(H_2O_2\), \(Na_2O_2\))
• \( -\frac{1}{2} \) in superoxides

Peroxides contain an O–O single bond, which changes the oxidation state of oxygen.
Step 1: {Consider hydrogen peroxide as an example.} \[ H_2O_2 \] The oxidation state of hydrogen is \(+1\). Let the oxidation state of oxygen be \(x\).
Step 2: {Apply the rule that total oxidation state equals zero for a neutral molecule.} \[ 2(+1) + 2x = 0 \] \[ 2 + 2x = 0 \] \[ 2x = -2 \] \[ x = -1 \]
Step 3: {State the result.} Thus, the oxidation state of oxygen in peroxides is \[ -1 \]