The nucleus of an atom consists mainly of which two particles?

The nucleus of an atom is primarily composed of protons and neutrons. Protons are positively charged particles that contribute to the atomic number and identity of an element, while neutrons are neutral particles that add mass to the atom and contribute to nuclear stability. Together, these two types of nucleons (protons and neutrons) make up the dense core of the atom.

Electrons are found outside the nucleus in electron shells or energy levels and have a negligible mass compared to protons and neutrons. Quarks are fundamental constituents of protons and neutrons; however, since the question specifically asks about the particles that make up the nucleus, protons and neutrons are the most relevant. Therefore, the correct answer highlights the fundamental components of the atomic nucleus and their roles within it.