Solution

In $$[Co(NH_3)_5CO_3]ClO_4$$, five ammonia ligands and one carbonate ligand is attached to the central cobalt atom. Hence, the coordination number is six.

Let X be the oxidation number of cobalt. $$X+(-2)+(-1)=0$$ or $$X=3$$. Hence, the oxidation number is 3.

The outer electronic configuration of cobalt (atomic number 27) is $$3d^74s^2$$. The outer electronic configuration of $$Co^{+3}$$ will be $$3d^64s^0$$. Thus it contains six d electrons.

$$[Co(NH_3)_5CO_3]ClO_4$$ is inner orbital or low spin complexes. all the electrons are paired due to $$d^2sp^3$$ hybridization of $$Co^{+3}$$ ion. Hence, the number of unpaired d electrons is zero.