Worked example: Build the proton and neutron from quarks and verify their charges; then check a beta-decay quark transition. Step 1: Proton = uud: charge = 2/3 + 2/3 − 1/3 = +1. ✓ Step 2: Neutron = udd: charge = 2/3 − 1/3 − 1/3 = 0. ✓ Step 3: Beta-minus decay at quark level: d → u + e⁻ + anti-ν_e (a down quark becomes up via the weak force). Step 4: Charge check: −1/3 → +2/3 − 1 − 0 = −1/3. ✓ (The W⁻ boson carries away the −1 difference.) Step 5: So neutron (udd) → proton (uud) + electron + antineutrino — the familiar beta decay is one quark changing flavour. Conclusion: everyday matter is just three quark flavours plus electrons — and radioactivity is quarks changing identity via the weak force.