In the atomic spectrum of hydrogen,the series of lines observed in the visible region is:

The energy of an electron in the second Bohr orbit of a hydrogen atom is:

The shortest wavelength in the hydrogen spectrum is approximately (in $nm$)

The energy of an electron in a hydrogen atom in its ground state is $-13.6 \ eV$. The energy of the level corresponding to the quantum number equal to $5$ is ............. $eV$.

The wavelength of a spectral line for an electronic transition is inversely related to :

Explain: Photoelectric effect.