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:

20) The wavelengths of electron waves in 2 orbits is 3 : 5. The ratio of kinetic energy of electrons will be: