Final answer:
A positively charged particle in the nucleus of an atom is the proton, which along with neutrons, constitutes the nucleus and defines the atomic number of an element.
Step-by-step explanation:
The positively charged particle in the nucleus of an atom is the proton. Protons, along with neutrons, make up the nucleus. Neutrons have no charge and are therefore neutral, but the presence of protons gives the nucleus its positive charge. Protons have a mass of 1 and a charge of +1, which contributes to the overall charge of the atom. The number of protons in an atom's nucleus determines the atomic number, which defines the type of element the atom represents.
In addition to protons and neutrons, known collectively as nucleons, electrons are negatively charged particles that orbit the nucleus, contributing to the atom's charge balance. However, the mass of an electron is significantly less than that of a proton or neutron. Specifically, the proton's mass is approximately 1836 times that of an electron, and a neutron is slightly more massive than a proton.