Helium is the lightest noble gas and the second most abundant element (after hydrogen) in the universe.
(a) The radius of a helium atom is 3.1x10⁻¹¹ m; the radius of its nucleus is 2.5x10⁻¹⁵ m. What fraction of the spherical atomic volume is occupied by the nucleus (V of a sphere = \left.\frac{4}{3} \pi r^{3}\right) ?
