Which subatomic particle did j j thomason discover and what did this lead him to postulate about the nature of the atom?

Answer 1

The electron. Originally called cathode rays.

Answer 2

J.J. Thomson discovered the electron in 1897. This led him to propose the "plum pudding" model of the atom, where electrons were embedded in a positively charged sphere, suggesting that atoms were not indivisible as once thought.