Question

Which of the following species is paramagnetic ?

• A. NO–
• B. O22–
• C. CN–
• D. CO

Answer 1

Answer: (A)

NO–

Answer 2

(1) NO– is derivative of O2 and isoelectronic with O2.

So ($\sigma$1s)2 ($\sigma$ *1s)2 ($\sigma$2s)2 ($\sigma$ *2s)2 ($\sigma$2pz)2 ($\pi$2p2x = $\pi$2p2y ) ($\pi$ *2px1 = $\pi$ *2p1y) and 2 unpaired electrons.

(2) O22– : ($\sigma$1s)2 ($\sigma$ *1s)2 ($\sigma$2s)2 ($\sigma$ *2s)2

($\sigma$2pz)2 ($\pi$2p2x = $\pi$2p2y ) ($\pi$ *2px2 = $\pi$ *2p2y) and no unpaired electrons.

(3) CN– is derivative of and isoelectronic with N2 : ($\sigma$1s)2 ($\sigma$ *1s)2 ($\sigma$2s)2 ($\sigma$ *2s)2 ($\pi$2p2x = $\pi$2p2y ) ($\sigma$2pz)2 and no unpaired electron.

(4) CO is derivative of and isoelectronic with N2 : ($\sigma$1s)2

($\sigma$ *1s)2 ($\sigma$2s)2 ($\sigma$ *2s)2 ($\pi$2p2x = $\pi$2p2y ) ($\sigma$2pz)2 and no unpaired electron.