Question

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Answer 1

1) 1. Rutherford

2. Rutherford's alpha scattering experiment: He directed a stream of alpha particles towards a very thin gold foil. He observed that most of the particles went straight through the foil but some were slightly deflected and very few were either deflected by large angles or bounced back.

2) Conclusions of Rutherford's experiment:
1. The atom contains a large empty space.
2. There is a positively charged mass at the center of the atom known as the nucleus.
3. The electrons revolve around the nucleus at large distances from the nucleus. 
4. An atom as a whole is electrically neutral. 

3) Atomic number: The number of electrons or the number of protons in an atom is called atomic number.

Mass number: The number of protons along with the number of neutrons is called mass number.

Electron: An electron may be defined as a sub-atomic particle having a unit negative charge and a mass equal to 1/1837 of a hydrogen atom.