Answer: alpha particles bouncing off gold foil
Step-by-step explanation:
Rutherford gave an experiment known as gold foil experiment.
In his experiment, he took a gold foil and bombarded it with alpha particles which are basically helium nuclei carrying positive charge. He thought that the particles will pass straight through the foil, but to his surprise, many of them passed through, some of them deflected their path and a few of them bounced back.
From this he concluded that in an atom, there exist a small positive charge in the center. Due to this positive charge, the alpha particles deflected their path and some of them bounced straight back their path as like repels like.
Bohr in his structure of atom explained that electrons revolve around the nucleus in fixed orbit or shell or energy levels.These energy levels are stable and have fixed energy values. When an electron absorbs energy , it moves to a higher energy state and when gets back to its original ground state, it emits energy which gives the line spectra.