Show that the density of a nucleus does not depend on its mass number. Estimate its value.

How to lay out the answer. Follow the frame, then write it in your own words.

1 · Write the radius formula. R = r₀∛A, with r₀ = 1.2 × 10⁻¹⁵ m.
2 · Find the volume. V = (4/3)πR³ = (4/3)πr₀³A.
3 · Write the mass. M ≈ Am, where m = 1.67 × 10⁻²⁷ kg is the mass of one nucleon.
4 · Divide. ρ = M/V = 3m/(4πr₀³): A cancels.
5 · Put in the numbers. ρ = 3 × 1.67 × 10⁻²⁷ ÷ (4 × 3.14 × 1.728 × 10⁻⁴⁵) ≈ 2.3 × 10¹⁷ kg m⁻³.
6 · Real life. Neutron stars have roughly this density.
7 · Close in one line. So, all nuclei have the same, enormous density.

Scoring tip: Show clearly that A cancels; that line carries the mark. Give the unit kg m⁻³ with your answer.