(i) sp³ , tetrahedral, paramagnetic
(ii) dsp², square planar, diamagnetic
(iii) d²sp³, octahedral, paramagnetic

Ligands have different field strength and as a result the crystal field splitting, \({ \Delta }_{ 0 }or{ \Delta }_{ t }\)depends upon the field produced by the ligand and charge on metal ions. Some ligands are strong and able to produce strong field; whereas others are weak and able to produce weak field. The series of ligands in which ligands are arranged in increasing order of field strength is called spectrochemical series, e.g.
 \(({ I }^{ - }<{ Br }^{ - }<{ Cl }^{ - }<{ { SCN }^{ - } }<{ F }^{ - }<{ OH }^{ - }<{ { C }_{ 2 }{ O }_{ 4 } }^{ - }<{ H }_{ 2 }O<{ NCS }^{ - }<{ EDTA }^{ 4- }<{ NH }_{ 3 }\)
Weak field ligand cannot cause pairing of electrons and will form high spin complex/whereas stron$ field ligand can cause pairing of electrons and will form low spin complex.

In both the complexes, Fe is in +3 oxidation state with the configuration 3d⁵. CN- is a strong ligand. In its presence, 3d electrons pair up leaving only one unpaired electron. The hybridization is d 2sp³forming inner orbital complex. H₂0 is a weak ligand. In its presence, 3d electrons do not pair up. The hybridization is sp³ d²  forming an outer orbital complex containing five unpaired electrons. Hence, it is strongly paramagnetic.

Stability of coordination compounds in aqueous solution is determined with the help of satbility constant. Higher the value of stability constant, greater will be stability. Smaller the cation, higher the charge on the cation, more stable will be the complex. Chelating agents form more stable complex than monodentate ligand. Stronger the ligand, more stable will be the complex.

(i)The chemical formula of the compound is shown. Its name is cis-diammine dichlorido platinum (II).
(ii) It behaves as an anti cancer agent by taking part in the chelate formation or chelation.
(iii) In the trans isomer the similar groups are on opposite sides and chelate formation does not take place.
(iv) Cis-platin saves many valueable lives by forming co-ordinate complex. So it is life saving.

When white light falls on the complex, some part of it is absorbed.  Greater the CFSE, greater is the energy absorbed or shorter is the wavelength absorbed \((E={hc\over\lambda })\).  The observed colour is the complementary colour of the colour absorbed.

(i) As isomer A reacts with AgNO₃ to give a white precipitate, CI must be present in the ionization sphere. As it does not react with BaCI₂, SO₄^2- must be present in coordination sphere.
Formula of A = [Co(NH₃)₅SO₄] CI (coordination no. of Co = 6) As reactions are reverse for isomer B, formula of B = [Co(NH₃)₅CI]S0₄
(ii) Ionization isomerism.
(iii) A = Pentaarnminesulphatocobalt (III) chloride ; B = Pentaamminechloridocobalt (ill) sulphate