Correct option is (D) \(\frac{R^2}{r^2}\sqrt{\frac{H}g}\)
We know that, time to empty a container if orifice at the bottom
t = \(\frac{A}{A_0}\sqrt{\frac{2H}{g}}\)
given \(\because H = H/2\)
t = \(\frac{\pi R^2}{\pi r^2}\sqrt{\frac{2H/2}g}\)
Where A0 = area of orifice
t = time
t = \(\frac{R^2}{r^2}\sqrt{\frac{H}g}\)