The area of the region bounded by the curve $y=\sqrt{a^2-x^2}$ and x-axis included between the lines x = 0 and x = a is

$\frac{a^2}{4}$ units $\pi a^2$ units $4 \pi$ units $\frac{\pi a^2}{4}$ units

$\frac{\pi a^2}{4}$ units

The correct answer is Option (4) - $\frac{\pi a^2}{4}$ units