What is the wavelength of the least energetic photon emitted in the Lyman series of the hydrogen atom spectrum? (in $nm$)

In a hydrogen atom,when an electron transitions from the fourth orbit to the ground state,find the wavelength of the emitted photon in $nm$.

The wavelength of light for the least energetic photons emitted in the Lyman series of the hydrogen spectrum is nearly. [Take $hc = 1240 \text{ eV-nm}$, change in energy of the levels $= 10.2 \text{ eV}$] (in $\text{ nm}$)

If radiation of all wavelengths from ultraviolet to infrared is passed through hydrogen gas at room temperature,absorption lines will be observed in the:

In the spectrum of hydrogen,the ratio of the longest wavelength in the Lyman series to the longest wavelength in the Balmer series is

Let the series limit for the Balmer series be $\lambda_{1}$ and the longest wavelength for the Brackett series be $\lambda_{2}$. Then $\lambda_{1}$ and $\lambda_{2}$ are related as: