Final answer:
The oil drop experiment conducted by Robert Millikan proved the existence of electrons.
Step-by-step explanation:
The oil drop experiment conducted by Robert Millikan proved the existence of electrons.
Millikan observed the movement of charged oil droplets between metal plates with a potential applied to oppose the gravitational force. By adjusting the electric field strength and making careful measurements, he was able to determine the charge on individual drops. This experiment provided the first accurate direct measurement of the charge on electrons, confirming their existence.