The fundamental particle which has no charge and has mass almost equal to that of positively charged fundamental particle is neutron.

Neutrons are neutral. 

The mass of an atom is given by the sum of the masses of protons and neutrons present in the nucleus.

Neutron is represented as "n" as it does not have any charge.

The three subatomic particles of atom are: electrons, protons and neutrons.

In the year $1932$ James Chadwick discovered neutrons. He bombarded lighter elements like boron and beryllium by alpha particles.

The neutron is a subatomic particle with no net electric charge and a mass slightly larger than that of a proton. Protons and neutrons, each with mass approximately one atomic mass unit, constitute the nucleus of an atom, and they are collectively referred to as nucleons.

James Chadwick was assigned the task of tracking down evidence of Rutherford's tightly bound "proton-electron pair" or neutron. In 1932, Chadwick proposed that this particle was Rutherford's neutron. In 1935, he was awarded the Nobel Prize for his discovery.

Chadwick concluded that the mass of the emitted particle is similar to that of proton. Mass of proton is 1.0072766 a.m.u. and that of neutron is 1.0086654 a.m.u.

Chadwick carried the experiments, using many different elements as radiation targets besides paraffin. What really occurred when one bombarded beryllium with alpha particles, there was the formation of a carbon-12 nucleus and the emission of a neutron.

Chadwick was able to prove that the neutral particle could not be a photon by bombarding targets other than hydrogen.

James Chadwick discovered the neutron.

Initially it was believed that the atom consisted of a small massive nucleus with positive charge surrounded by a much larger cloud of negatively charged electrons. Being charge-less particle, neutron did not show their influence in experiments performed for discovery of charged particles electrons and protons.

Neutrons were discovered by bombarding beryllium with alpha particles. James Chadwick discovered the neutron in 1932 while working at Cavendish Laboratory.

In 1930 it was discovered that Be bombarded by alpha particles and emitted stream of radiation. In 1932 Chadwick proposed that the particle is Rutherford's neutron.

Protons in neutral atom = nuclear charge = 11

Chadwick was able to prove that the radiation causing the ejected particles was much more energetic than could be accounted for by photons. Initially it was though that the radiation must be gamma rays. But the radiations differed in interaction with hydrocarbons and with elements like helium, lithium, carbon, oxygen, nitrogen etc.

When one bombarded beryllium with alpha particles, a carbon-12 nucleus was formed and a neutron was emitted.
$ _4^9Be + _2^4He \rightarrow _6^{12}C + _0^1n$

Chadwick carried out the experiments, using many different elements as radiation targets besides paraffin. By comparing the energies of particles ejected from all these various targets, Chadwick was able to prove that the radiation causing the ejected particles was much more energetic than could be accounted for by photons.

Mass of neutron is 1.0086654 a.m.u. Neutron is 1842 times heavier than an electron.

The presence of neutron and its mass was determined by James Chadwick. Neutron was discovered by bombarding $\alpha-$particles on $Be$. On doing so, highly energetic beam of radiation was observed by Chadwick. Thus mass of neutron was determined by James Chadwick.

The $\alpha-$ ray scattering-gold foil experiment by Ernest Rutherford gave substantial evidence for  existence of nucleus in $1911$. Thus the existence of nucleus was proved by Rutherford's experiment.

 Neutron was discovered by Chadwick.
To overcome the failure of proton electron hypothesis, Rutherford, in 1920, proposed the existence of neutral particle made from close combination of proton and electron. He named it neutron.
In 1932, Lord Chadwick proved the existence of neutron by bombarding lighter elements (boron and beryllium) with alpha particles which resulted in the emission of highly penetrating neutral radiation.