Why is the neutron neutral?

Answer 1

The neutrality of the neutron is a matter of definition; since it behaves as uncharged, it is categorized as such. The definition could be attributed to extensive experimental observations which ultimately contributes to the current broad scientific consensus, and thus it is ultimately admitted to a Standard Model wherein its charge neutrality becomes canonical. This is the essence of the scientific process. However, this is not to say the causality behind lack of charge is therefore self-evident; charge is a property of matter, and if a particle lacks the property, one might ask, why does it lack that particular property?

In the case of the neutron, it is a composite particle made up of smaller fundamental particles, called quarks. Quarks themselves are the only particles in the Model assigned a fractional value of the fundamental charge; in the case of the neutron, two (down) quarks with charges of negative one third are bound in a trio with a third (up) quark of positive two thirds; the sum of the three equals zero (2/3 - 1/3 - 1/3 = 0), and thus the neutron exhibits overall electrical neutrality, or zero charge.

Answer 2

The neutron is neutral because it is composed of one negatively charged electron and two positively charged up quarks and one negatively charged down quark, which cancels out the charges to create a neutral particle.