Question

why the cathode rays always are consider to be consists of fundamental comon particle called electron ?​

Answer 1

This is because cathode rays have natively charged particles in them...
(This can be concluded by various experiments done in the past like when cathode rays are passed in a tube and positively charged particles are placed near to its path then it was found that these rays got attracted to it and whereas when negatively charged substance was kept then these rays for deflected)....
Since cathode rays have negatively charged particles therefore they contain electrons in them...

Hope it helps....

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