ACS Chemistry Practice Exam 2025 – The All-in-One Guide to Exam Success!

Millikan's oil drop experiments were pivotal in determining the charge of the electron, which is foundational to our understanding of atomic structure and electrical phenomena. By carefully measuring the forces acting on tiny charged oil droplets suspended in an electric field, Millikan was able to calculate the charge on individual droplets. Through extensive experimentation, he established that the charge of the electron is approximately -1.6 x 10^-19 coulombs. This discovery confirmed that electric charge is quantized and provided a direct measurement of the electron's charge, a significant step forward in both physics and chemistry.

The other choices, while important in their own right, are not related to Millikan's findings. The mass of the neutron, the structure of the atom, and the speed of light were determined by other experiments and scientists. Thus, the work of Millikan remains specifically associated with quantifying the charge of the electron.