The ratio of the radii of the third orbit of He⁺ to the second orbit of Li²⁺ is: (r₁ for H = 5.29 × 10⁻¹¹ m)
r₃(He⁺)/r₂(Li²⁺) ≈ 3.375.
Ref: NCERT Class 11 Chemistry > Chapter 2: Structure of Atom > Topic: Developments Leading to Bohr Model - Electromagnetic Radiation and Spectrum