(i) Coordination entity is an ion or a neutral molecule, composed of a central atom, usually a metal and the array of other atoms or groups of atoms (ligands) that are attached to it. In the formula, the coordination entity is enclosed in square brackets.
(ii) For example, in potassium ferrocyanide, K₄[Fe(CN)₆], the coordination entity is [Fe(CN)₆]^4-.

(i) Porphyrin
(ii) Cobalt
(iii) Wilkinson Catalyst [(PPh₃)₃ RhCl]

(i) CFSE is higher when the complex contains strong field ligand as per spectro chemical series.
(ii) Thus, crystal field splitting energy increases in the order 
[CrCI₆]^3- <   [Cr(NH₃)₆]³⁺ <  [Cr(CN)₆]^3-, Because the order of field strength is Cl^- < NH³ < CN^-

(i)  [Cr(C₂O₄)₃]^3- - It does not possess geometrical isomerism.
(ii) [CO(NH₃)₃Cl₃] - Two geometrical isomers are possible.

Magnetic moment (μ) = \(\sqrt { n(n+2) } \) BM
Fe (z = 26) = 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶
Fe²⁺ = 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s⁰

∴μ =  \(\sqrt { n(n+2) } \) = \(\sqrt { 4(4+2) } =\sqrt { 24 } \) 
= 4. 89 BM  

K₃[Fe(C₂O₄)₃]

Tetraammine copper (II) sulphate.

Ligand is an atom or a group of atoms which is either negatively charged or has lone pair of electrons and from co-ordinate bond with the central metal or ion, e.g.H₂O.

Hexaqua Nickel Chloride

Six

Monochloro is (ethane-1, 2-diamine) nitrito- K O Cobalt (III) chloride.

\({ }_{22} \mathrm{Ti}-{ }_{18}[\mathrm{Ar}] 4 \mathrm{s}^{2} 3 \mathrm{d}^{2} / {}_{21}\mathrm{Sc}-{ }_{18}[\mathrm{Ar}] 4 \mathrm{~s}^{2} 3 \mathrm{~d} \)
\({ }_{22} \mathrm{Ti}^{3+}-{ }_{18}[\mathrm{Ar}] 3 \mathrm{~d}^{1} /{ }_{18} \mathrm{Sc}^{3+}{ }_{18}[\mathrm{Ar}] 3 \mathrm{~d}^{0}\)
(i) In this complex the central metal ion is Ti³⁺, which has d¹ configuration. This single electron occupies one of the t_2g orbitals in the octahedral aqua ligand field. When white light falls on this complex the electron absorbs light and promotes itself to e_g level. The spectral data show the absorption maximum is at 20000 cm^-1 corresponding to the crystal field splitting energy \(\left(\Delta_{o}\right)\) 239.7 kJmol^-1. The transmitted colour associated with this absorption is purple and hence the complex appears purple in colour.
(ii) Thus in \(\left[\mathrm{Ti}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+} \mathrm{d}-\mathrm{d}\) transition takes place.
(iii) But in \(\left[\mathrm{Sc}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+} \mathrm{Sc}^{3+}\) has the outer electronic configuration of 3d⁰ where d-d transition is not possible and it is colourless.

(i) \(\mathrm{Mg}\left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right) \mathrm{Cl}_{5}\right]^{2-} \rightleftharpoons \mathrm{Mg}^{2+}+\left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right) \mathrm{Cl}_{5}\right]^{2-} (2 ions)\)
(ii) \(\begin{aligned} {\left[\mathrm{Cr}\left(\mathrm{NH}_3\right)_5 \mathrm{Cl}_3\left[\mathrm{CoF}_6\right]_2 \rightleftharpoons 3\right.} & {\left[\mathrm{Cr}\left(\mathrm{NH}_3\right)_5 \mathrm{Cl}\right]^{2+} } \\ & (5 \text { ions }) \end{aligned}\)\(+2\left[\mathrm{CoF}_6\right]^{3-}\)
(iii) \(\left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{3} \mathrm{Cl}_{3}\right]= \text{ No ions}\)
If no of ions increases, molar conductivity increases molar conductivity of the complex also INCREASES.
\(\therefore\) The order of the given compound is
[Cr(NH₃)₃Cl₃]<Mg[Cr(NH₃)₃Cl₃] < [Cr(NH₃)₅Cl₃] [CoF₆]₂
  (No ion)          (2 ions)                    (5 ions)

[Co (en)₂ Cl₂]⁺ This is an octahedral complex

\(\text {(a) }\left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{6}\right]^{3+}:{ }_{24} \mathrm{Cr} \Rightarrow{ }_{18}[\mathrm{Ar}] 4 \mathrm{~s}^{2} 3 \mathrm{~d}^{4} \)
\({ }_{21} \mathrm{Cr}^{3+} \Rightarrow{ }_{18}[\mathrm{Ar}] 3 \mathrm{~d}^{3}\)

(i) d²sp³ hybridisation (octahedral)
(ii) It has three unpaired electrons (n = 3)
(iii) So it is paramagnetic
(iv) Magnetic moment \(\left(\mu_{\mathrm{s}}\right)=\sqrt{\mathrm{n}(\mathrm{n}+2)} \mathrm{BM}\)
\(=\sqrt{3(3+2)}=\sqrt{15}=3.87 \mathrm{BM}\)
\((b) \ \left[\mathrm{Ni}(\mathrm{CN})_{4}\right]^{2-:}{ }_{28} \mathrm{Ni} \Rightarrow[\mathrm{Ar}] 4 \mathrm{~s}^{2} 3 \mathrm{~d}^{8} ;{ }_{26} \mathrm{Ni}^{2+} \Rightarrow{ }_{18}[\mathrm{Ar}] 3 \mathrm{~d}^{8}\)

(i) dsp² hybridisation
(ii) Geometry - square planar
(iii) No unpaired electrons- It is Diamagnetic
(iv) Magnetic moment (μ_s) = 0.