15) If the shortest wavelength of H atom in Lyman series is a, then the longest wavelength in Balmer series of He⁺ is:

16) When in a H atom, electron falls from infinity to stationary state 1, the wavelength of radiation emitted would be:

17) According to Bohr theory, the angular momentum of an electron in 5^th orbit is:

18) The ratio of ionisation energy of He and Be³⁺ is:

19) The relative penetrating power of α, β, γ and neutron (n) follows the order: