Question

What are some examples of Oxidation numbers ?

Answer 1

To solve the given question, we should have knowledge about oxidation numbers and how to calculate it. Oxidation Number, is the number of electrons gained or lost or shared to form a compound from an element.
Some general rules that follow oxidation number are that the oxidation number of a free element is always $0$, the oxidation number of a Group $1$ element in a compound is $+1$ , a Group $2$ element in a compound is $+2$ and the sum of oxidation numbers of all of the atoms in a compound is of total charge of the molecule.

Complete answer:
The first example we could look forward to was the oxidation number of $Cr$ in $CrCl_3$ . Let the oxidation number of Chromium be $x$ . We can say that the total charge or molecule is zero.
$x-3=0$
$x=+3$
Therefore, the oxidation number of $Cr$ in $CrCl_3$ is $+3$ .
Next one can be $KCl$ , so, oxidation number of $Cl$ is $-1$ . While in the case of $Cl_2$ , it is $0$ . In $KClO_2$ , the oxidation number of $Cl$ is $+3$.
In case of $KMnO_4$ , the oxidation number of $Mn$ is ;
Let the oxidation number of $Mn$ be $x$ . The oxidation number of the molecule as a whole is $0$ .
So, it can be calculated as :
$+1+x-8=0$
$x=+7$
So, the oxidation number of $Mn$ in $KMnO_4$ is $+7$ .

Note:
While calculating the oxidation number the charge on the whole molecule should be duly noted and identified. This is a crucial step which should not be messed up to find the correct oxidation state.