What particle did Chadwick discover in 1932 that was hard to detect because it had no electrical charge?

Neutron

Explanation:

Neutron is a sub-atomic particle which does not have any charge. It is present in the nucleus of an atom along with the protons. Both protons and neutrons are responsible for mass of an atom. Neutrons were hard to detect because of lack of electric charge. In an experiment, he bombarded Beryllium with alpha particles, high energy radiation was released which was not deflected by magnetic field. On studying more properties, the particle was named as neutron.