What is the oxidation state of \[Co\] in the complex ${{[Co{{({{H}_{2}}O)}_{5}}Cl]}^{2+}}$
A. 2
B. 3
C. 1
D. 4

Hint: The complex is a cationic complex . Here water is a neutral ligand and chlorine is a negative ligand. By summing the charges of the ligands we can calculate the oxidation state of the central atom.

Complete Step by Step Solution:
Here the given complex is ${{[Co{{({{H}_{2}}O)}_{5}}Cl]}^{2+}}$.
Here two types of ligands are attached to the central metal atom that is cobalt. The ligands are five water ligands and one chloride ligand.

Let the oxidation state of $Co$ is $x$ .
As water is a neutral ligand so, the charge on water is $0$ .
Again chloride is a negative ligand so, the charge of chloride ligand is $-1$ .
The overall charge of the given complex is $+2$ .

Thus we can write as follows:
$ x+0\times 5+(-1)=+2 \\ $
$ x-1=2 \\ $
$ x=+3 \\ $

So, the value of $x$ by solving the above equation is $+3$ .
So, the oxidation state of the central metal atom cobalt is also $+3$ .
Thus the correct option is B.

Additional information: Cobalt is a transition element. In the $+3$ oxidation state the metal $d$ orbital has $6$ electrons and acts as an oxidising agent.

Note: Thus cobalt have low electron density and easily accepts electrons and acts as a oxidizing agent. Here cobalt exist as a high spin complex.