CBSE Class 9 Answered

In 1932, James Chadwick observed that when beryllium was exposed to α-particles, different kinds of particles were emitted. These particles had about the same mass as protons and carried no electrical charge. Hence, Chadwick named this particle as neutron. It was present in the nucleus along with the proton. A neutron is represented by letter n. Neutrons are present in the nucleus of all the atoms except hydrogen. As protons and neutrons are both present in the nucleus, they are together known as nucleons.