How many spectral lines are obtained when an electron transitions from the $8^{th}$ orbit to the $1^{st}$ orbit in a hydrogen atom?

The wavelength of the radiation emitted,when in a hydrogen atom an electron falls from infinity to stationary state $n = 1$,would be ........ $nm$ (Rydberg constant $R_H = 1.097 \times 10^7 \ m^{-1}$)

The distance between the $4^{th}$ and $3^{rd}$ Bohr orbits of $He^{+}$ is $:-$

Explain the energy of a photon,the kinetic energy of an ejected electron,and the number of photons in the photoelectric effect.

What is the energy associated with the first orbit of $Li^{2+}$ $(R_{H} = 2.18 \times 10^{-18} \ J)$?

According to Bohr's model,the energy of an electron is given by $E = -\frac{2.176 \times 10^{-18}}{n^2} \, J \, atom^{-1}$. Calculate the minimum energy required to remove an electron from the $3^{rd}$ orbit of a $He^{+}$ ion,and also calculate the corresponding wavelength of the photon.