$\frac{\sqrt{2}}{3}$ is a rational number.

There are infinitely many integers between any two integers.

Number of rational numbers between $15$and $18$ is finite.

There are numbers which cannot be written in the form $\frac{p}{q}, q\ne 0, p, q$ both are integers.

The square of an irrational number is always rational.

$\frac{\sqrt{12}}{\sqrt{3}}$ is not a rational number as $\sqrt{12}$ and $\sqrt{3}$ are not integers.

$\frac{\sqrt{15}}{\sqrt{3}}$ is written in the form $\frac{p}{q},$ where $p, q$ are integers and $q\ne 0$. So, it is a rational number.

Classify the following number as rational or irrational with justification:

$\sqrt{196}$

Classify the following number as rational or irrational with justification:

$3\sqrt{18}$