Proton was discovered by Goldstein...... electrons was discovered by jj Thomson and neutrons was discovered by james chadwick................

Atom:
The concept of atoms can be traced back to ancient Greece, where the idea of the atom as the fundamental building block of matter was introduced by the philosopher Democritus around 400 BCE. However, it wasn't until the early 19th century that significant progress was made in understanding the nature of atoms.

John Dalton:
English chemist John Dalton is credited with formulating the atomic theory in the early 1800s. He proposed that all matter is composed of tiny, indivisible particles called atoms, which combine to form compounds in fixed ratios. Dalton's atomic theory laid the foundation for the modern understanding of atoms.

Nucleus:
The discovery of the atomic nucleus is attributed to the work of Ernest Rutherford and his colleagues around the early 20th century. Rutherford conducted a series of experiments, including the famous gold foil experiment, to investigate the structure of atoms.

Ernest Rutherford:
Ernest Rutherford, a New Zealand-born physicist, conducted the gold foil experiment in 1909. In this experiment, Rutherford bombarded a thin sheet of gold foil with alpha particles (helium nuclei). According to the prevailing model at the time, the Thomson model, it was expected that the alpha particles would pass through the foil with minimal deflection. However, Rutherford observed that some of the alpha particles were deflected at large angles and even bounced back. This unexpected result led him to propose the existence of a dense, positively charged nucleus at the center of an atom.

Proton:
In 1919, Rutherford, together with his colleagues Hans Geiger and Ernest Marsden, conducted further experiments to investigate the nature of the atomic nucleus. They performed experiments involving the bombardment of nitrogen gas with alpha particles and observed the emission of hydrogen nuclei (protons). This discovery led to the identification of the proton as a subatomic particle within the nucleus, carrying a positive charge.

Neutron:
James Chadwick, an English physicist and student of Rutherford, is credited with the discovery of the neutron in 1932. Chadwick conducted experiments involving the bombardment of beryllium with alpha particles, which resulted in the emission of a neutral particle with a mass similar to that of a proton. This neutral particle was identified as the neutron, a subatomic particle located within the atomic nucleus, carrying no electrical charge.

In summary, the concept of the atom was introduced by Democritus, and John Dalton formulated the atomic theory. Ernest Rutherford discovered the atomic nucleus, while James Chadwick discovered the neutron. These discoveries, made through various experiments, revolutionized our understanding of the fundamental building blocks of matter.