Match the compounds given in Column I with the oxidation state of cobalt present in it (given in Column II) and assign the correct code.

Column I (Compound)	Column II (Oxidation state of Co)
A. [Co(NCS)(NH3)5(SO3)]	1. + 4
B. [Co(NH3)4Cl2]SO4	2. 0
C. Na4[Co(S2O3)3]	3. +1
D. [Co2(CO)8]	4. +2
	5. +3

Code 

(i) A (1)     B (2)      C (4)      D (5)

(ii) A (4)    B (3)      C (2)      D (1) 

(iii) A (5)   B (1)      C (4)      D (2) 

(iv) A (4)   B (1)      C (2)      D (3)

CoCl₃.NH₃ + AgNO₃ $\stackrel{}{\to }AgC\mathcal{l}\downarrow \left(2mol\right)$  

$\left[Co{\left(N{H}_3\right)}_{5}C\mathcal{l}\right]C{\mathcal{l}}_2+AgN{O}_3\stackrel{}{\to }AgC\mathcal{l}\downarrow \left(2mol\right)$  

x = 5

In H₂O (polar solvent) dibromophenol derivative and in CS₂ (non-polar solvent moneobromo phenol derivate is obtained.

3d => 4d => 5d CFSE increases for the same ligands.

Factual
⇒ leaching methods is used for those metal in which metal is more soluble than impurities and these are Al, Au, Ag, low grade Cu

σ bonded organometallic compound ⇒ M – C
σ-bond
and in π – bonded organo metallic compound
M – C
π bond
In ferrocene, there is π-bond