Species Having One Unpaired Electron

Question:
The total number of species from the following in which one unpaired electron is present, is _________.

N₂, O₂, C₂⁻, O₂⁻, O₂²⁻, H₂⁺, CN⁻, He₂⁺

Correct Answer: 4

Explanation (Molecular Orbital Theory)

Species having one unpaired electron show paramagnetic behaviour.

• N₂: All electrons paired → Diamagnetic

• O₂: Two unpaired electrons → Not counted

• C₂⁻: One unpaired electron → Counted

• O₂⁻: One unpaired electron → Counted

• O₂²⁻: All electrons paired → Diamagnetic

• H₂⁺: One electron → Unpaired → Counted

• CN⁻: All electrons paired → Diamagnetic

• He₂⁺: One unpaired electron → Counted

Total species having exactly one unpaired electron = 4

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