A hydrogen atom in its ground state is irradiated by light of wavelength 970Å. Taking hc/e=1.237×10⁻⁶eV m and the ground state energy of hydrogen atom as -13.6eV, the number of lines present in the emission spectrum is:

The electron in the ground state of H-atom jumps to the nth state after absorbing the radiation.Wavelength of the radiation, λ=970Å=970×10⁻¹⁰mEnergy gained by the electron,E'=hc/eλ eV=1.237×10⁻⁶/970×10⁻¹⁰=12.75eVThus the energy of the nth state,En=-13.6+12.75=-0.85eVUsing: En=-13.6/n²eV ∴ -0.85=-13.6/n² ⇒n=4Number of (emission) spectral line,N=n(n-1)/2=4(4-1)/2=6lines