We are asked to determine the charge of a proton, an electron, and a neutron. The charges of these particles are considered constant. The proton is a particle that is located in the nucleus of an atom and its charge is:

Where "e" is the elementary charge and is equivalent to:

The unit of charge is "C" and it is called "Coulombs".
In the case of the neutron, this is also a particle that is located in the nucleus of the atom but this particle carries no charge, therefore, the charge of a neutron is:

In the case of the electron, this is a sub-atomic particle with a negative charge. The charge of the electron is:

This means the negative of the elementary charge.