Option 1 states that oxidation involves the loss of electrons, while reduction involves the gain of electrons. This statement is correct.
Option 2 states that oxidation involves the gain of electrons, while reduction involves the loss of electrons. This statement is incorrect. The correct statement is provided in Option 1.
Option 3 states that an oxidizing agent decreases the oxidation number, while a reducing agent increases the oxidation number. This statement is incorrect. The correct statement is that an oxidizing agent increases the oxidation number, while a reducing agent decreases the oxidation number.
Option 4 states that an oxidizing agent increases the oxidation number, while a reducing agent reduces the oxidation number. This statement is correct.
Therefore, the correct statements regarding oxidation and reduction are:
1. In oxidation, loss of electrons takes place, whereas in reduction, gain of electrons takes place.
4. An oxidizing agent increases the oxidation number, while a reducing agent reduces the oxidation number.
The correct answer is Option 4.