25 the chemical process in which electrons are gained by an atom or an ion is called(1) addition (3) reduction
(2) oxidation (4) substitution

Option (3) is the correct answer.

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.