Match the compounds given in Column I with the oxidation state of

cobalt has given in column II and assigns the correct code.

 Column I (Compound) Column II (Oxidation state of Co) A.$\left[\mathrm{Co}\left(\mathrm{NCS}\right){\left({\mathrm{NH}}_{3}\right)}_{5}\right]\left({\mathrm{SO}}_{3}\right)$ 1. +4 B.$\left[\mathrm{Co}{\left({\mathrm{NH}}_{3}\right)}_{4}{\mathrm{Cl}}_{2}\right]{\mathrm{SO}}_{4}$ 2.  +2 C.${\mathrm{Na}}_{4}\left[\mathrm{Co}{\left({\mathrm{S}}_{2}{\mathrm{O}}_{3}\right)}_{3}\right]$ 3. 0 D.$\left[C{o}_{2}{\left(CO\right)}_{8}\right]$ 4.  +3

Codes

A          B          C           D

1.       2          3           4           1

2.       3          1           5           2

3.       5          4           3           2

4.       4          1           2           3

Hint: Oxidation state of CO ligand is zero

Calculate the oxidation state of CO in different complexes as follows:

A. $\left[\mathrm{Co}\left(\mathrm{NCS}\right){\left({\mathrm{NH}}_{3}\right)}_{5}\right]\left({\mathrm{SO}}_{3}\right)$

Let oxidation state of Co is x.

$+2=-1+5×0+\mathrm{x}\phantom{\rule{0ex}{0ex}}\mathrm{x}=+2+1=+3$

B. $\left[\mathrm{Co}{\left({\mathrm{NH}}_{3}\right)}_{4}{\mathrm{Cl}}_{2}\right]{\mathrm{SO}}_{4}$

Let oxidation state of Co is x

c. ${\mathrm{Na}}_{4}\left[\mathrm{Co}{\left({\mathrm{S}}_{2}{\mathrm{O}}_{3}\right)}_{3}\right]$

Let oxidation state of Co is x

$X+3×\left(-2\right)=-4\phantom{\rule{0ex}{0ex}}x-6=-4\phantom{\rule{0ex}{0ex}}x=-4+6=+2$

D.$\left[C{o}_{2}{\left(CO\right)}_{8}\right]$

Let oxidation state of Co is x

$x-8×0=0\phantom{\rule{0ex}{0ex}}x=0$

Hence, option 4th is the correct answer.