4. which hypothesis led to the discovery of the proton?
a. cathode rays should be attracted to a positively-charged plate.
b. the nucleus of an atom should contain neutrons.
c. when a neutral hydrogen atom loses an electron, a positively-charged
particle should remain.
d. a proton should be 1840 times heavier than an electron.

Option C.When a neutral hydrogen atom loses an electron, a positively-charged .

Explanation: When a neutral hydrogen atom loses an electron a positively charged particle must remain.  Proton is a positive charge of +1 e charge with a mass that is slightly less than that of a neutron. Ernest Rutherford discovered that a atom must have a concentrated positive charge at the center that contains most of the atom's mass. He stated that the nucleus contained a positive charge the proton. And the weight of a proton is 1837 times heavier than the weight of the electron.

Result: Losing of an electron by hydrogen lefts a positive charge i.e proton.