Electrically charged Hg drops fall from certain height 4R, where R is the radius of a metallic fixed sphere on the non conducting floor. In the top most portion of the sphere there is a small opening as shown in the figure, $q,m$ are charge and mass of each drop, acceleration due to gravity is $g$, then

Maximum number of drops that can enter the sphere is  $\frac{6\pi {\epsilon }_{0}mg{R}^2}{q^2}$

Charged drops fall freely and acquire the speed $2\sqrt{gR}$ when they reach the top most point of the sphere

Succeeding drops reach the top most of the sphere with lesser speed as compared to preceding one

Maximum number of drops that can enter the sphere is  $\frac{12\pi {\epsilon }_{0}mg{R}^2}{q^2}$