Which of the following is a rational number?

Explanation

1. 01

   $(2 + \sqrt{3})(2 - \sqrt{3}) = 4 - 3 = 1$, which is rational.

2. 02

   $(1 + \sqrt{2})^2 = 3 + 2\sqrt{2}$, irrational.

3. 03

   $\sqrt{3} + \sqrt{12} = \sqrt{3} + 2\sqrt{3} = 3\sqrt{3}$, irrational.

4. 04

   $\frac{\sqrt{18}}{\sqrt{3}} = \sqrt{6}$, irrational.