Question

Peroxide ion is

• A. Paramagnetic
• B. Ferromagnetic
• C. Diamagnetic
• D. Antiferromagnetic

Hint:

Diatomic species with an even total number of electrons are usually diamagnetic, with the famous exceptions of \( \text{B}_2 \) (10 electrons) and \( \text{O}_2 \) (16 electrons), which are paramagnetic due to Hund's rule filling of degenerate orbitals. Since \( \text{O}_2^{2-} \) has 18 electrons, it is strictly diamagnetic.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
We need to determine the magnetic behavior (paramagnetic or diamagnetic) of the peroxide ion (\( \text{O}_2^{2-} \)).

Step 2: Key Formula or Approach:
We will apply Molecular Orbital (MO) Theory to find the electronic configuration of the diatomic species \( \text{O}_2^{2-} \) and count the number of unpaired electrons.

Step 3: Detailed Explanation:
1. The peroxide ion is \( \text{O}_2^{2-} \).
2. Total number of electrons = \( 2 \times 8 \text{ (from O atoms)} + 2 \text{ (negative charge)} = 18 \text{ electrons} \).
3. The molecular orbital electronic configuration for an 18-electron diatomic species is:
\[ \sigma_{1s}^2 \ \sigma_{1s}^{*2} \ \sigma_{2s}^2 \ \sigma_{2s}^{*2} \ \sigma_{2p_z}^2 \ \pi_{2p_x}^2 \ \pi_{2p_y}^2 \ \pi_{2p_x}^{*2} \ \pi_{2p_y}^{*2} \]
4. Since all the molecular orbitals (including the anti-bonding \( \pi^* \) orbitals) are completely filled with paired electrons, there are no unpaired electrons present in the peroxide ion.
5. A species with zero unpaired electrons is diamagnetic.

Step 4: Final Answer:
The peroxide ion is diamagnetic, which corresponds to option (C).