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NCERT Class XII Chemistry
Chapter - Coordination Compounds
Questions with Solutions

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Question : 19 of 43
Marks: +1, -0
[Cr(NH3)6]3+[\mathrm{Cr}(\mathrm{NH}_3)_6]^{3+} is paramagnetic while [Ni(CN)4]2−[\mathrm{Ni}(\mathrm{CN})_4]^{2-} is diamagnetic. Explain why?
Solution:  
[Cr(NH3)6]3+:Cr(24):[Ar]4s13d5,[\mathrm{Cr}(\mathrm{NH}_3)_6]^{3+} : \mathrm{Cr}(24) : [\mathrm{Ar}] 4s^1 3d^5,
Cr3+(21):[Ar]4s03d3\mathrm{Cr}^{3+}(21) : [\mathrm{Ar}] 4s^0 3d^3
is paramagnetic due to presence of unpaired electrons
[Ni(CN)4]2−:Ni(28):4s23d8,[\mathrm{Ni}(\mathrm{CN})_4]^{2-} : \mathrm{Ni}(28) : 4s^2 3d^8,
Ni2+:4s03d8\mathrm{Ni}^{2+} : 4s^0 3d^8
It has square planar shape and is diamagnetic due to absence of unpairedelectrons.
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