Complex sentence: In quantum mechanics, a group of particles known as fermions (for example, electrons, protons and neutrons) obey the Pauli exclusion principle, which states that no two fermions can occupy the same (one-particle) quantum state.
Split into simpler sentences: In quantum mechanics, a group of particles known as fermions (for example, electrons, protons and neutrons) obey the Pauli exclusion principle. This states that no two fermions can occupy the same (one-particle) quantum state.