A number of the form $\dfrac{p}{q}$ is said to be a rational number if

1. $p \text{ and } q$ are whole numbers and $q ≠ 0$.

2. $p$ is a whole number and $q$ is a natural number.

3. $p \text{ and } q$ are integers and $q ≠ 0$.

4. $p \text{ and } q$ are integers and $p ≠ 0, q ≠ 0$.

The numbers which can be expressed in the form $\dfrac{p}{q}$, where $p \text{ and } q$ are integers and $q ≠ 0$, are called rational numbers.

The numerator $p$ may also be 0, as $\dfrac{0}{q} = 0$ is a rational number, but the denominator $q$ can never be 0 since division by 0 is not defined.

Hence, Option 3 is the correct option.