Ionization potential of hydrogen atom is 13.6 eV. Hydrogen atoms in the ground state are excited by monochromatic radiation of photon energy 12.1 eV. According to Bohr's theory, the spectral lines emitted by hydrogen will be

Ionization energy corresponding to ionizationpotential = -13.6 eVPhoton energy incident = 12.1 eVSo, the energy of electron in excited state= -13.6 + 12.1 = -1.5 eV⇒En=−13.6n2eV−1.5=−13.6n2n2=−13.6−1.5≈9      ∴n=3That is energy of electron in excited state corresponds to third orbit.The possible spectral lies are when electron jumps form orbit 3rd to 2nd; to 1st and 2nd to 1st. Thus, 3 spectral lines are emitted.