Which of the following phenomena suggests the presence of electron energy levels in atoms?

If energy of $15 \ eV$ is given to an electron in the $4^{th}$ orbit,find its final energy when it comes out of the $H$-atom. (in $eV$)

Find the ratio of energies of photons produced due to the transition of an electron in a hydrogen atom from its $(i)$ second permitted energy level to the first level,and $(ii)$ the highest permitted energy level to the first permitted level.

The ionization potential of a hydrogen atom is $13.6 \text{ eV}$. How much energy needs to be supplied to ionize a hydrogen atom in the first excited state (in $\text{ eV}$)?

If the electron in a hydrogen atom moves from the ground state orbit to the $5^{\text{th}}$ orbit,then the potential energy of the electron

According to the Bohr atom model,in which of the following transitions will the frequency be maximum?