Question

Why was neutrons discovered so late?

Answer 1

A neutron is hard to detect partly because it has no charge, which means they are only detected when they collide with the nucleus of an atom. Such detectors as Geiger Counters can pick up ionizing that does not require such an actual collision, so some other types of particles are much easier to detect. 


That's why they were discovered at last..
Hope it helps you buddy..

Answer 2

Electrons and protons were able to be discovered because they have electrical charges. ... Neutrons were the last particle to be discovered because they had no charge to detect. Scientists assumed that there was a neutral particle, but couldn't describe it yet.