Define isotopes, isobars and isotones, giving one example of each.

1. 1 · Recall the numbers. Z = protons, A = nucleons, N = A − Z = neutrons.
2. 2 · Isotopes. Same Z, different A: ³⁵₁₇Cl and ³⁷₁₇Cl. Same element, same chemistry.
3. 3 · Isobars. Same A, different Z: ⁴⁰₁₈Ar and ⁴⁰₂₀Ca. Different elements.
4. 4 · Isotones. Same N, different Z and A: ²³₁₁Na and ²⁴₁₂Mg (N = 12).
5. 5 · Real life. Carbon-14 (an isotope) dates old fossils; deuterium makes heavy water for reactors.
6. 6 · Close in one line. So, isotopes share protons, isobars share mass number and isotones share neutrons.

Scoring tip: Always write Z and A on your examples; an example without them scores less.