What is an emission line?

For a certain hypothetical one-electron atom,the wavelength (in $\mathring{A}$) for the spectral lines for transition from $n = p$ to $n = 1$ is given by $\lambda = \frac{1500p^2}{p^2 - 1}$ (where $p > 1$). The ionization potential of this element must be ......$V$ (Take $hc = 12420 \text{ eV-} \mathring{A}$).

What is the ratio of the total energy of an electron in a hydrogen atom in the first excited state to that in the third excited state?

An electron jumps from the $5^{th}$ orbit to the $4^{th}$ orbit of a hydrogen atom. Taking the Rydberg constant as $10^7 \ m^{-1}$,what will be the frequency of the radiation emitted?

If the ionization energy of a hydrogen atom in the ground state is $13.6 \ eV$,find the ionization potential of the third orbit in $eV$.

The total energy of an electron in the ground state of a hydrogen atom is $-13.6 \text{ eV}$. The kinetic energy of an electron in the first excited state is.....$\text{ eV}$