Question

How did jj thomson arrive at the conclusion that matter was made of electrons

Answer 1

Thomson in his plum pudding model had predicted that an atom consists of an evenly charged positive sphere and some negatively charged particles scattered on it.
The thing is that everything in this nature wants to achieve a state of equilibrium. Also atoms are electrically neutral.So acc. to him if there is positive charge in an atom, there must an equal no. of positive charge to to make an atom electrically neutral.