The question is incomplete, here is the complete question:
The smallest unit of charge is - 1.6 × 10⁻¹⁹ C, which is the charge in coulombs of a single electron.
Robert Millikan was able to measure the charge on small droplets of oil by suspending them between a pair of electrically charged plates. Which of the following are possible charges of those oil droplets?
A. - 1.2 × 10⁻¹⁹ C
B. - 3.2 × 10⁻¹⁹ C
C. - 4.8 × 10⁻¹⁹ C
D. - 5.6 × 10⁻¹⁹ C
E. - 8.0 × 10⁻¹⁹ C
F. - 9.4 × 10⁻¹⁹ C
<u>Answer:</u> The possible charges of the oil droplets are
,
and 
<u>Explanation:</u>
Millikan’s oil drop experiment is used to measure the charge of an electron. Before this experiment, the subatomic particles were not accepted.
He found that all the oil drops had charges that were the multiples of
. This value is the charge on 1 electron
Number of electrons excess electrons is calculated by using the formula:

From the given options:
- <u>Option A:</u>


As, the excess electron is not a whole number. So, this charge cannot be taken as the charge on an oil drop.
- <u>Option B:</u>


As, the excess electron is a whole number. So, this charge can be taken as the charge on an oil drop.
- <u>Option C:</u>


As, the excess electron is a whole number. So, this charge can be taken as the charge on an oil drop.
- <u>Option D:</u>


As, the excess electron is not a whole number. So, this charge cannot be taken as the charge on an oil drop.
- <u>Option E:</u>


As, the excess electron is a whole number. So, this charge can be taken as the charge on an oil drop.
- <u>Option F:</u>


As, the excess electron is not a whole number. So, this charge cannot be taken as the charge on an oil drop.
Hence, the possible charges of the oil droplets are
,
and 