Answer: Option (3) is the correct answer.
Step-by-step explanation:
In the process of oxidation, an atom loses electrons or an increase in oxidation number of the atom occurs.
For example,
is an oxidation process.
Whereas in a process of reduction, an atom gain electrons or a decrease in oxidation number of the atom occurs.
For example,
is a reduction process.
Thus, we can conclude that the chemical process in which electrons are gained by an atom or an ion is called reduction.