Problem 90

Given information

 Millikan’s oil drop consist of charge  

Step-by-step explanation

Millikan's oil drop experiment states that the charge of each oil drop is the integral multiple of the smallest charge, which is the charge of an electron, number of the excess electrons is the integral multiple

The charge of an electron is measured by Millikan's oil drop experiment.

An excess drop is equal to the negative charges

An excessive charge is total charge divided by one negative charge 

is the one negative charge associated with an electron as per Millikan Oil Drop Experiment