To solve this problem we will apply the concepts related to the electric field such as the smelting of the Force and the load (In this case the force is equivalent to the weight). Later we will apply the ratio of the total charge as a function of the multiplication of the number of electrons and their individual charge.
Here,
m = mass
g = Acceleration due to gravity
Rearranging to find the charge,
Replacing,
Since the field is acting upwards the charge on the drop should be negative to balance it in air. The equation to find the number of electrons then is
Here,
n = Number of electrons
e = Charge of each electron
Replacing,
Therefore the number of electrons that reside on the drop is