$2\sqrt{3} + \sqrt{3}$ is equal to

1. $2\sqrt{6}$
2. 6
3. $3\sqrt{3}$
4. $4\sqrt{6}$

The value of $\sqrt{8} + \sqrt{18}$

1. $\sqrt{26}$
2. $2(\sqrt{2} + \sqrt{3})$
3. $5\sqrt{2}$
4. $6\sqrt{2}$

If x is a positive rational number which is not a perfect square, then $-5\sqrt{x}$ is

1. a negative integer
2. an integer
3. a rational number
4. an irrational number

If x, y are both positive rational numbers, then $(\sqrt{x} + \sqrt{y})(\sqrt{x} - \sqrt{y})$ is

1. a rational number
2. an irrational number
3. neither rational nor irrational number
4. both rational as well as irrational number