Millikan's Oil Drop experiment and Photoelectric effect

Millikan's oil drop experiment established that

In the Millikan’s Oil Drop experiment, the oil drop is subjected to such forces whose nature does NOT fall under the category of:

In Millikan's oil drop experiment an oil drop carrying a charge Q is held stationary by a potential difference 2400 V between the plates. To keep a drop of half the radius stationary the potential difference had to be made 600 V . What is the charge on the second drop ?

A non-monochromatic light is used in an experiment on photoelectric effect. The stopping potential

which of the following experiment in Photoelectric effect will support particle nature of light?

An oil drop of radius 2 mm with a density 3 g cm^(-3) is held stationary under a constant electric field 3.55 xx 10^5 V m^(-1) in the Millikan's oil drop experiment. What is the number of excess electrons that the oil drop will possess ? Consider g=9.81 m//s^2