Question

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

• A. $\left[Zn\right(N{H}_3{)}_6{]}^{2+}$
• B. $\left[Cr\right(N{H}_3{)}_6{]}^{3+}$
• C. $\left[Co\right(N{H}_3{)}_6{]}^{3+}$
• D. None of the above

Answer 1

The correct option is C $\left[Co\right(N{H}_3{)}_6{]}^{3+}$

ln $\left[Co\right(N{H}_3{)}_6{]}^{3+}$, oxidation state of $Co=+3$ and its co-ordination number is six.
So ${}_{27}Co-1s^2,2s^2,2p^6,3s^{2}3p^6,3d^7,4s^2$
$C{o}^{3+}-1s^2,2s^2,2p^6,3s^{2}3p^6,3d^6$ln $\left[Co\right(N{H}_3{)}_6{]}^{3+}$ shows inner orbital complex as well as diamagnetic in behaviour (due to absence of upaired electron).
$\left[Zn\right(N{H}_3{)}_6{]}^{3+}\to s{p}^3{d}^2$ hybridisation outer orbital complex and diamagnetic.
$\left[Cr\right(N{H}_3{)}_6{]}^{2+}\to d^{2}s{p}^3$ hybridisation inner orbital complex and paramagnetic.