Non superimposable mirror images are called optical isomers and may be described as “chiral’. They are also called enantiomers and rotate plane polarised light in opposite directions.

$${K_3}\left[ {Fe{{\left( {CN} \right)}_6}} \right]$$   is potassium hexacyano ferrate (III).

$$Hg{I_2}\left( s \right) + 2{I^ - }\left( {aq} \right) \to {\left[ {Hg{I_4}} \right]^{2 - }}\left( {aq} \right)$$

In $${\left[ {Co{{\left( {N{H_3}} \right)}_6}} \right]^{3 + }},$$   oxidation state of $$Co = + 3$$   and its coordination number is six.
$$\eqalign{ & _{27}Co = 1{s^2},2{s^2}2{p^6},3{s^2}3{p^6}3{d^7},4{s^2} \cr & C{o^{3 + }} = 1{s^2},2{s^2}2{p^6},3{s^2}3{p^6}3{d^6} \cr} $$

$${\left[ {Co{{\left( {N{H_3}} \right)}_6}} \right]^{3 + }}$$   is an inner orbital 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 complex and diamagnetic in nature ).
$${\left[ {Cr{{\left( {N{H_3}} \right)}_6}} \right]^{3 + }} \to {d^2}s{p^3}$$     hybridisation ( inner orbital complex and paramagnetic in nature ).

Shape of $${\left[ {Cu{{\left( {N{H_3}} \right)}_4}} \right]^{2 + }}$$   is square planar.

$$E.C.\,{\text{of}}\,C{r^{3 + }}\left( {3{d^3}} \right):$$    
For complex A $${\left[ {Cr{{\left( {{H_2}O} \right)}_2}} \right]^{3 + }}:$$

For complex B $${\left[ {Cr{{\left( {N{H_3}} \right)}_6}} \right]^{3 + }}:$$

Here, both the complexes $$\left( A \right)\,{\text{and}}\,\left( B \right)$$   are paramagnetic with $$3$$ unpaired electrons each. Also $$H2O$$  is a weak field ligand which causes lesser splitting than NH3 which is comparatively stronger field ligand. Hence, the $$\left( {D0} \right)$$  value of $$\left( A \right)\,{\text{and}}\,\left( B \right)$$   are calculated from the wavelengths of light absorbed and not from the wavelengths of light emitted.

No explanation is given for this question. Let's discuss the answer together.

Due to some backbonding by sidewise overlapping of between $$d{\text{ - orbitals}}$$   of metal and $$p{\text{ - orbitals}}$$   of carbon, the $$Fe - C$$  bond in $$Fe{\left( {CO} \right)_5}$$  has both $$\sigma $$  and $$\pi $$  character.

The correct name is chlorobis ( ethylenediamine ) nitritocobalt (III).

As number of stable rings increases stability of complex compound also increases due to chelation effect.
Number of rings in $${\left[ {Ni{{\left( {en} \right)}_2}} \right]^{2 + }} = 2$$
Number of rings in $$\left[ {Ni{{\left( {dmg} \right)}_2}} \right] = 4$$