What is the number of waves formed by an electron in the $5^{th}$ Bohr orbit of a hydrogen atom?

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:

Which of the following statements regarding the $H$ atom spectrum is correct?

If the energy of a photon with a frequency of $2 \times 10^{12} \ Hz$ is $E$,then the energy of a photon with a frequency of $4 \times 10^{12} \ Hz$ will be ....

The emission spectrum of a gaseous atom is line-based and not continuous. Why?

With increasing Principal Quantum number,the energy difference between adjacent energy levels in $H$ atom: