(a) It is the figure of α -particle scattering experiment (gold foil experiment). 

(b) In this experiment, a stream of high energy α – particles from a radioactive source was directed at a thin foil of gold metal which had a circular fluorescent zinc sulphide screen around it. Whenever αparticles struck the screen, a tiny ash of light was produced at that point. The α- particles striking the gold foil were analysed. 

It was observed that: 

1. Most of the α – particles passed through gold foil undeflected. 

2. A small fraction of the α – particles are deflected by small angles. 

3. A very few α – particles(1 in 20,000) bounced back i.e., deflected by nearly 180°.

c) Rutherford drew the following conclusions regarding the structure of atom from this experiment: 

1. Most of the space in the atom is empty as most of the α – particles passed through the foil undeflected. 

2. The positive charge of the atom is concentrated in a very small volume (called nucleus) that repelled and deflected the positively charged α – particles.

3. Volume occupied by the nucleus is negligibly small as compared to the total volume of the atom.