If an electron in the excited state falls to the ground state,a photon of energy $5 \ eV$ is emitted. The wavelength of the photon is nearly: (in $nm$)

Due to transitions among its first three energy levels,a hydrogenic atom emits radiation at three discrete wavelengths $\lambda_1, \lambda_2$ and $\lambda_3$ (where $\lambda_1 < \lambda_2 < \lambda_3$). Then,

Energy levels $A$,$B$ and $C$ of a certain atom correspond to increasing values of energy,i.e.,$E_A < E_B < E_C$. If $\lambda_1$,$\lambda_2$,and $\lambda_3$ are the wavelengths of the photons corresponding to the transitions shown in the figure,then:

The four lowest energy levels of an $H$-atom are shown in the figure. The number of possible emission lines would be

The energy levels with transitions for an atom are shown in the figure. The transitions corresponding to the emission of radiation of maximum and minimum wavelength are respectively:

The ratio of energies of photons produced due to transition of an electron in a hydrogen atom from the second energy level to the first energy level and from the fifth energy level to the second energy level is: