Species Having One Unpaired Electron

Question:
Number of molecules/species from the following having one unpaired electron is _________.

O₂, O₂⁻, NO, CN⁻, O₂²⁻

Correct Answer: 2

Explanation (Molecular Orbital Theory)

• O₂: Has two unpaired electrons → paramagnetic (not counted).

• O₂⁻: Has one unpaired electron → paramagnetic ✔

• NO: Odd electron species, one unpaired electron ✔

• CN⁻: All electrons paired → diamagnetic.

• O₂²⁻: All electrons paired → diamagnetic.

Hence, number of species having exactly one unpaired electron = 2.

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