Charge on an electron was first dertermined by:

Options

A. Millikan
B. Bohr
C. Thomson
D. Rutherford.

Answer

To determine the charge on an electron, we need to identify the scientist who first measured or calculated this value. The charge of an electron is known to be approximately \(1.6 \times 10^{-19}\) Coulombs.

1. **Identify the Scientists**: We need to consider the contributions of various scientists in the field of atomic physics. Notable figures include J.J. Thomson and Niels Bohr.

2. **J.J. Thomson's Contribution**: J.J. Thomson is known for his work with cathode rays and for discovering the electron. He conducted experiments that led to the determination of the charge-to-mass ratio of the electron, but he did not directly measure the charge itself.

3. **Robert Millikan's Experiment**: The charge on the electron was first accurately measured by Robert Millikan through his famous oil drop experiment conducted in 1909. In this experiment, he balanced the gravitational and electric forces on tiny charged oil droplets to determine the charge of the electron.

4. **Conclusion**: Therefore, the charge on an electron was first determined by Robert Millikan.

### Final Answer:
The charge on an electron was first determined by Robert Millikan.