The charge is quantized, this is shown by:

Millikan's Oil drop experiment: 

• In this experiment, Milliken allowed charged tiny oil droplets to pass through a hole into an electric field.
• By varying the strength of the electric field the charge over an oil droplet was calculated, which always came as an integral value of charge on one electron.

Davisson-Gomer's experiment:

• Initially, the atomic models proposed by various scientists could only explain the particle nature of electrons but failed to explain their wave nature.
• In the year 1927 C.J. Davisson and L.H. Germer perform an experiment, which is known as Davisson Germer’s experiment by which they explain the wave nature of electrons through electron diffraction.

Compton scattering experiment:

• Compton effect is defined as the effect that is observed when x-rays or gamma rays are scattered on a material with an increase in wavelength.
• Arthur Compton studied this effect in the year 1922.
• During the study, Compton found that wavelength is not dependent on the intensity of incident radiation.
• It is dependent on the angle of scattering and on the wavelength of the incident beam.

Raman effect: Raman effect is defined as the scattering of photons by the excited molecules that are at higher energy levels.