Which type of particle obeys the Pauli exclusion principle?

Fermions are the type of particles that obey the Pauli exclusion principle. They have half-integer spin and cannot share an identical quantum state.

The principle applies to elementary fermions such as electrons, quarks, and neutrinos, as well as composite particles such as protons and neutrons. In an atom, it prevents two electrons from having the same complete set of quantum numbers. This restriction creates electron shells and helps produce the structure of the periodic table.

Bosons, by contrast, have integer spin and are not subject to the Pauli exclusion principle. Many identical bosons can occupy the same quantum state; lasers and Bose–Einstein condensates rely on this different behavior.

A common mix-up is treating leptons or quarks as alternatives to fermions. Leptons and quarks are both categories of elementary fermions, so they do obey the principle. The most general answer is therefore fermions. The deeper reason comes from the spin-statistics theorem, which connects half-integer spin with antisymmetric quantum wavefunctions.