An oxidation process involves:
A. Increase in oxidation number
B. Decrease in oxidation number
C. Both decrease and increase in oxidation number
D. No change in oxidation number

Hint: In a chemical reaction there are two types of process involved. One is oxidation and another is reduction. Generally metals undergo oxidation easily. The chemicals which are involved in the chemical reaction have to undergo either oxidation or reduction process.

Complete step by step answer:
- The oxidation is a process in which an increase in oxidation number of the element happens with the loss of electrons.
- For better understanding about the oxidation process see the below example.
\[{{\underset{+2}{\mathop{Cu}}\,}^{2+}}+\underset{0}{\mathop{Zn}}\,\to \underset{0}{\mathop{Cu}}\,+{{\underset{+2}{\mathop{Zn}}\,}^{2+}}\]
- In the above reaction copper accepts electrons from zinc and zinc donates its electrons to copper.
- Means copper undergoes reduction (gain of electrons) and zinc undergoes oxidation (loss of electrons).
- Therefore in the oxidation process (consider the above mentioned example) the zinc element is going to change its oxidation number from zero (0) to +2 and copper is going to change its oxidation number from +2 to zero.
- Means in the oxidation process the oxidation number of elements increases.
So, the correct option is A.

Note: Oxidation means not only loss of electrons. So many definitions are there for oxidation.
Addition of oxygen to an element is called oxidation.
Removal of hydrogen from a chemical or element is called oxidation.
Whatever the definition of oxidation among the above mentioned, the common thing that we will observe is the oxidation number of the particular element increases after the oxidation process.