(a) When a coordination compound $ ext{CoCl}_3 \cdot 6 ext{NH}_3$ is mixed with excess of $ ext{AgNO}_3$ solution, $3$ moles of $ ext{AgCl}$ are precipitated per mole of the compound. Write the structural formula of the complex, IUPAC name, its hybridisation and magnetic behaviour on the basis of valence bond theory. OR (b) (i) How many geometrical isomers are possible in each of the following complexes ? (I) $[ ext{Cr}( ext{C}_2 ext{O}_4)_3]^{3-}$ (II) $[ ext{Co}( ext{NH}_3)_3 ext{Cl}_3]$ (ii) $[ ext{Co}( ext{NH}_3)_6]^{3+}$ is an inner orbital complex whereas $[ ext{Ni}( ext{NH}_3)_6]^{2+}$ is an outer orbital complex. Why ? [Atomic number : $ ext{Co} = 27, ext{Ni} = 28$] (iii) Write the formula of Wilkinson catalyst and its use.