Which hypothesis led to the discovery of the proton?

When a neutral hydrogen atom loses an electron a positively charged particle should remain. A proton is a subatomic particle, symbol p+, with a positive charge of + 1e elementary charge and mass slightly less than that of a neutron.

Ernest Rutherford discovered that the atom must have a concentrated positive center charge that contains most of the atom's mass. He suggested that the nucleus contained a particle with a positive charge the proton.