State the number which is a whole number but not a natural number.

Insert a rational number and an irrational number between the following:
$0.15$ and $0.16$

If $x = 2 + \sqrt{3},$ then find the value of $x^{2} + \frac{1}{x^{2}}$ and $x^{3} + \frac{1}{x^{3}}.$

Classify the following numbers as rational or irrational with justification:
$(i)$ $-\sqrt{0.4}$
$(ii)$ $\frac{\sqrt{12}}{\sqrt{75}}$

For each question,select the proper option from four options given,to make the statement true: $\sqrt{5^{2}+12^{2}}$ is a / an $\ldots \ldots$ number.

Fill in the blanks to make the following statement true: $\sqrt{2} \cdot \sqrt{3} \cdot \sqrt{6} = \dots$