I) The energy of hydrogen atom in ground state is correctly -13.6 eV, according to Bohr's theory.
II) Using Bohr's radius formula, \( r_n = n^2 a_0 \), where \( a_0 = 0.529 \) Å, for \( n=3 \), the radius is \( 9 \times 0.529 = 4.761 \) Å = 476.1 pm, not 158.7 pm. So II is incorrect.
III) For hydrogen-like ions, the radius decreases as nuclear charge \( Z \) increases. Hence, the radius order is \( {H} (Z=1) >{He}^+ (Z=2) > {Li}^{2+} (Z=3) >{Be}^{3+} (Z=4) \). Statement III is correct.
The angular momentum of an electron in a stationary state of \(Li^{2+}\) (\(Z=3\)) is \( \frac{3h}{\pi} \). The radius and energy of that stationary state are respectively.