Question

Which one of the following is an inner orbital complex as well as diamagnetic in behaviour? (At. no. of $Zn=30,Cr=24,Co=27,Ni=28$)

• A. $[Zn(N{H}_3{)}_6{]}^{2+}$
• B. $[Cr(N{H}_3{)}_6{]}^{3+}$
• C. $[Co(N{H}_3{)}_6{]}^{3+}$
• D. $[Ni(N{H}_3{)}_6{]}^{2+}$

Answer 1

Answer: (C)

In ${\left[Co{\left(N{H}_3\right)}_6\right]}^{3+}$, oxidation state of $Co=+3$ and its coordination number is six.
${}_{27}Co=1s^2,2s^{2}2p^6,3s^{2}3p^{6}3d^7,4s^2$
$C{o}^{3+}=1s^2,2s^{2}2p^6,3s^{2}3p^{6}3d^6$

${\left[Co{\left(N{H}_3\right)}_6\right]}^{3+}$ is an inner otbital complex as well as diamagnetic in behaviour (due to absence of unpaired electrons).
${\left[Zn{\left(N{H}_3\right)}_6\right]}^{2+}\to s{p}^3{d}^2$ hybridisation (outer orbital and diamagnetic).
${\left[Cr{\left(N{H}_3\right)}_6\right]}^{3+}\to d^{2}S{p}^3$ hybridisation (inner orbital and paramagnetic).