How many emission spectral lines are possible when a hydrogen atom is excited to the $n$th energy level?

The energy of the orbit of hydrogen is $E_n = \frac{1.31 \times 10^6}{n^2} \ J \ mol^{-1}$. If an electron transits from $n = 3$ to $n = 2$,find the frequency of the emitted radiation. (Note: $h = 6.6 \times 10^{-34} \ J \ s$,$N_A = 6.02 \times 10^{23} \ mol^{-1}$)

What is the packet of energy called?

Calculate the radius of the fourth orbit of the $B^{4+}$ ion. (in $pm$)

When a photon of energy $12.75 \, eV$ is completely absorbed by a hydrogen atom in its ground state,the principal quantum number of the excited state will be:

The total number of spectral lines observed when an electron returns from the $6^{th}$ shell to the $2^{nd}$ shell in a hydrogen atom is: