Hydrogen atom in ground state is excited by a monochromatic radiation of λ= 975 Aο. Number of spectral lines in the resulting spectrum emitted will be

Energy of the photon, E=hcλE=6.63×10-34×3×108975×10-10 J=6.63×10-34×3×108975×10-10×1.6×10-19eV=12.75eVAfter absorbing a photon of energy 1275 eV, the electron will reach to third excited state of energy-0.85 eV, since energy difference corresponding to n =1 and n = 4 is 12.75 eV. ∴ Number of spectral lines emitted=(n)(n-1)2=(4)(4-1)2=6