What is the energy of an electron in the stationary state corresponding to $n=2$?

The shortest wavelength of hydrogen atom in Lyman series is $\lambda$. The longest wavelength in Balmer series of $He^{+}$ is

Two series of spectral lines of atomic hydrogen which do not belong to the infrared spectral region are

The number of maximum possible different spectral lines obtained in the Balmer series,when an electron makes a transition to the ground state from the $5^{th}$ excited state in a sample of hydrogen atoms,is:

In the transition of an electron in an atom,its kinetic energy changes from $y$ to $y/4$. The change in potential energy $(P.E.)$ will be:

The light of wavelength $242 \, nm$ is required to remove an electron from a $Na$ atom. What is the ionization energy of the sodium atom in $kJ \, mol^{-1}$?