Match the compounds given in List-I with the oxidation state of cobalt present in it given in List-II

Choose the correct answer from the options given below:

(A)-(I), (B)-(IV), (C)-(II), (D)-(III)

The correct answer is Option (4) → (A)-(I), (B)-(IV), (C)-(II), (D)-(III)

To find the oxidation state of Cobalt ($x$), we set the sum of all charges in the compound equal to zero.

(A) $[Co(NCS)(NH_3)_5](SO_3)$

• Ligands: $NCS^-$ ($-1$), $NH_3$ ($0$), $SO_3^{2-}$ ($-2$).
• Equation: $x + (-1) + 5(0) + (-2) = 0$
• Result: $x - 3 = 0 \rightarrow x = \mathbf{+3}$ (I)

(B) $[Co(NH_3)_4Cl_2]SO_4$

• Ligands: $NH_3$ ($0$), $Cl^-$ ($-1$), $SO_4^{2-}$ ($-2$).
• Equation: $x + 4(0) + 2(-1) + (-2) = 0$
• Result: $x - 4 = 0 \rightarrow x = \mathbf{+4}$ (IV)

(Note: While Co(+3) is more common, in this specific chemical formula with a sulfate counter-ion and two chlorides, the math dictates +4).

(C) $Na_4[Co(S_2O_3)_3]$

• Ligands: $Na^+$ ($+1$), $S_2O_3^{2-}$ ($-2$).
• Equation: $4(+1) + x + 3(-2) = 0$
• Result: $4 + x - 6 = 0 \rightarrow x = \mathbf{+2}$ (II)

(D) $[Co_2(CO)_8]$

• Ligands: $CO$ is a neutral carbonyl ligand ($0$).
• Equation: $2(x) + 8(0) = 0$
• Result: $x = \mathbf{0}$ (III)