Q.Briefly explain the elementary particles of nature.

Step 1. Historical background. Until roughly the 1960s, protons, neutrons and electrons were all believed to be genuinely fundamental particles, with nothing smaller inside any of them.

Step 2. The quark proposal and discovery. In 1964, Murray Gell-Mann and George Zweig independently proposed that protons and neutrons are, in fact, not fundamental, but are built from smaller constituents called quarks; this was confirmed experimentally in 1968 at the Stanford Linear Accelerator Center (SLAC).

Step 3. Quark flavours and charges. There are six known "flavours" of quark - up, down, charm, strange, top and bottom - each with a corresponding antiparticle, and every quark carries a fractional electric charge: the up quark carries $+\tfrac23e$, the down quark carries $-\tfrac13e$.

Step 4. Composition of the proton and neutron. A proton is built from two up quarks and one down quark, giving net charge $\tfrac23e+\tfrac23e-\tfrac13e=+e$, matching the proton's known charge; a neutron is built from one up quark and two down quarks, giving net charge $\tfrac23e-\tfrac13e-\tfrac13e=0$, matching its electrical neutrality. …

Trace the historical discovery of quarks, list the six flavours and their fractional charges, verify the proton/neutron compositions against their known …

• Forgetting to verify that the quark compositions actually reproduce the correct net charge for the proton (+e) and neutron (0) - this check is the key evidence the model works. …