Question

Which of the following is paramagnetic ? [2013]
(a) O₂⁻ (b) CN⁻
(c) NO⁺ (d) CO

Answer 1

To see which is paramagnetic we can see if the sum of valence electron

1) if the sum of valence electrons is odd then it is paramagnetic.

2) if the sum of valence electron is even then it is diamagnetic

Exception is that when sum of valence electrons is 6 or 12 then it will be paramagnetic.

Also if any compound has -ve charge then add that charge to total valence electrons and if it has +ve charge then subtract it from total valence electrons.

So from above

3) O₂⁻ = 13 valence electrons so it is paramagnetic

CN⁻ = 10 valence electrons so it is diamagnetic

NO⁺ = 10 valence electrons so it is diamagnetic

CO= 10 valence electrons so it is diamagnetic

4) So option (a) is correct answer

Answer 2

O₂⁻ is paramagnetic.

Explanation:

• Paramagnetism is a phenomenon where the ion or radicle responds to the magnetic field.

• Paramagnetism is seen because of the presence of unpaired electron in the species.

• So if the number of valance electrons of a compound is odd then it's paramagnetic.

• And if the number of valance electrons of a compound is even then it's diamagnetic.

• In O₂⁻, 13 valence electrons are present.

• So it is paramagnetic.

• In CN⁻, 10 valence electrons are present.

• So it is diamagnetic

• In NO⁺, 10 valence electrons are present.

• So it is diamagnetic.

• In CO, 10 valence electrons are present.

• So it is diamagnetic.

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