What experimental evidence did thomson have for each statement?
a. electrons have a negative charge.
b. atoms of all elements contain electrons.

Answer : In the experiment of Cathode Ray, Scientist J.J. Thomson found that a stream of electricity was attracted to the positive portion of an electrical plate, which helped him to conclude that there must be a negative aspect to matter. He called this discovery as the electron.

He was the one who suggested that these small, negatively charged particles were actually subatomic particles. Which are now called as "electrons".

Since atoms are found to be neutral, when it contain negatively charged electrons it must also contain some positively charged material.