The ratio of the radius of the first three Bohr orbits is

Calculate the energy and frequency of the radiation emitted when an electron jumps from $n = 3$ to $n = 2$ in a hydrogen atom.

How did Niels Bohr obtain detailed information regarding the structure of atoms and molecules?

Energy levels $A, B, C$ 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 radiations corresponding to the transitions $C$ to $B$,$B$ to $A$ and $C$ to $A$ respectively,which of the following statements is correct?

The ionization energy of sodium in $kJ \ mol^{-1}$,if electromagnetic radiation of wavelength $242 \ nm$ is just sufficient to ionize a sodium atom,is . . . . . . .

In the hydrogen spectrum,if an electron transitions from the $6^{th}$ orbit to the $3^{rd}$ orbit through multiple steps,what is the total number of spectral lines in the $U.V.$ region?