Nuclides, size, and density কী?

A nuclide $^{A}_{Z}\text{X}$ holds $Z$ protons and $N = A - Z$ neutrons, bound by the strong interaction: intense (${\sim}100\,\times$ Coulomb at contact), short-ranged (${\sim}1\,\mathrm{fm}$, felt only by touching neighbours), and blind to charge (it grips protons and neutrons alike). Scattering experiments give every nucleus the same recipe: radius

so volume grows like $A$ and the density is a universal $\rho \approx 2.3 \times 10^{17}\,\mathrm{kg}/\mathrm{m}^{3}$ — a raindrop of it would weigh like a fleet of tankers, and Chapter 27 will meet whole stars at this density. Isotopes share $Z$ but differ in $N$: same chemistry, different nuclear fates.