Match List I with List II List I List II A. [Co(NH_3)_5(NCS)](SO_3) I…

The correct answer is 3. A-IV, B-I, C-III, D-II.

List I	List II
A. \([Co(NH_3)_5(NCS)](SO_3)\)	IV. +3
B. \([Co(NH_3)_4Cl_2]SO_4\)	I. +4
C. \(Na_4[Co(S_2O_3)_3]\)	III. +2
D. \([CO_2(CO)_8]\)	II. 0

Let us  calculate the oxidation number of the central metal atom/ion in each of the given complexes:

A. \([Co(NH_3)_5(NCS)](SO_3)\):

Let the oxidation number of \(Co\) be \(x\)

We know,

Charge of \(NH_3\) ligand is \(0\)

Charge of \(NCS\) ligand is \(-1\)

Charge of \(SO_3\) ligand is \(-2\)

The overall charge of the complex should be \(0\)

Thus,

\(x + 5(0) + (-1) + (-2) = 0\)

or, \(x + 0 -1 -2 = 0\)

or, \(x - 3 = 0\)

or, \(x  = 3\)

Hence, the oxidation number of \(Co\) ion is \(+3\).

B. \([Co(NH_3)_4Cl_2]SO_4\):

Let the oxidation number of \(Co\) be \(x\)

We know,

Charge of \(NH_3\) ligand is \(0\)

Charge of \(Cl\) ligand is \(-1\)

Charge of \(SO_4\) ligand is \(-2\)

The overall charge of the complex should be \(0\)

Thus,

\(x + 4(0) + 2(-1) + (-2) = 0\)

or, \(x + 0 -2 -2 = 0\)

or, \(x - 4 = 0\)

or, \(x  = 4\)

Hence, the oxidation number of \(Co\) ion is \(+4\).

C. \(Na_4[Co(S_2O_3)_3]\):

Let the oxidation number of \(Co\) be \(x\)

We know,

Charge of \(Na\) is \(+1\)

Charge of \(S_2O_3\) ligand is \(-2\)

The overall charge of the complex should be \(0\)

Thus,

\( 4(1) + x + 3(-2) = 0\)

or, \(4 + x + -6 = 0\)

or, \(x - 2 = 0\)

or, \(x  = 2\)

Hence, the oxidation number of \(Co\) ion is \(+2\).

D. \([CO_2(CO)_8]\):

Let the oxidation number of \(Co\) be \(x\)

We know,

Charge of \(CO\) is \(0\)

Thus,

\(2x + 8(0) = 0\)

or, \(x = 0\)

Hence, the oxidation number of \(Co\) is \(0\).

So from these calculations it is clear that the correct answer is option 3. A-IV, B-I, C-III, D-II.