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Question:

Among [Ni(CO)4], [NiCl4]²⁻, [Co(NH3)4Cl2]Cl, Na3[CoF6], Na2O2 and CsO2, the total number of paramagnetic compounds is:

3

4

5

2

Solution:

[Ni(CO)4] 3d¹⁰, sp³ 0 unpaired electron
[NiCl4]²⁻ 3d⁸, sp³ 2
[Co(NH3)4Cl2]Cl 3d⁶, d²sp³ 0
Na3[CoF6] 3d⁶, sp³d² 4
Na2O2 O₂⁻² 0
CsO2 O₂⁻ 1