Question

Who was the discoverer of electrons?
A. J.J Thomson
B. Ernest Rutherford
C. James Chadwick
D. None of the above.

Answer 1

Electrons are the negatively charged subatomic particles, present in all the atoms. It is represented by ${e^ - }$ . Unlike protons and neutrons which are present inside the nucleus, electrons are present outside the nucleus revolving in the atomic orbitals.

Complete step by step answer: J.J Thomson was a British physicist, Born on $18$ December $1856$.
In the late $19^{th}$ century, he started experimenting with cathode ray tubes. Cathode rays tubes are sealed tubes, made up of glasses from which air is evacuated. He applied a high voltage across the electrodes of the tube. It caused the flow of a beam of particles from cathode (negative electrode) to anode (positive electrode). This is the reason that the tube is called the cathode rays tube as the beam of the particles or the "Cathode ray" originates from cathode.
To detect these particles, he painted the tube behind the anode with a phosphorescent material such as zinc sulphide. This caused a sparts, or emit when an electron strites on it
Further to test the properties of the particle J.J Thomson placed two electric plates of opposite charge around the cathode rays. The cathode ray got deflected from the negative plate and started moving towards the positive plate that showed that the cathode ray is composed of negatively charged particles, later named as electrons.

So, the correct answer is “Option A”.

Additional Information: In $1898$, J.J Thomson proposed the 'Thomas model of an atom'.
He proposed that the atom is spherical in shape, approximately ${10^{ - 10}}m$ in size. In the atom, the positive charge is evenly distributed and electrons are embedded in the positive cloud as seeds are embedded in watermelon (watermelon model) or plum in plum pudding (plum pudding model). Thus, he concluded that the atom is neutral as a whole.

Note: The electrons present in the atom counterbalances the positive charge in the atom, thus making it neutral. Electrostatic force of attraction is present between electrons and protons to tightly hold them together.