A particle is dropped vertically from rest, from a height. The time taken by it to fall through successive distance of 1 km each will then be:

All equal, being equal to $\sqrt{2/g}$  second

In the ratio of the square roots of the integers $1$ , $2$ , $3$ , $\dots$

In the ratio of the difference in the square roots of the integers, i.e., $\sqrt{1}$ , $\left(\sqrt{2}-\sqrt{1}\right)$ , $\left(\sqrt{3}-\sqrt{2}\right)$ , $\left(\sqrt{4}-\sqrt{3}\right)$ , $\dots$

In the ratio of the reciprocals of the square roots of the integers, i.e.,$\frac{1}{\sqrt{1}}$ , $\frac{1}{\sqrt{2}}$ , $\frac{1}{\sqrt{3}}$ ,$\dots$