The spectral series of the hydrogen atom that lies in the visible region of the electromagnetic spectrum is:

In a hydrogen sample,if the atoms are excited to states with principal quantum number $n = 20$,then the number of different wavelengths which may be observed in the spectrum is:

When an electron in a hydrogen atom jumps to the innermost orbit,the radiation emitted belongs to which one of the following series?

Ratio of longest wavelengths corresponding to Lyman and Balmer series in hydrogen spectrum is :-

What is the wavelength of light for the least energetic photon emitted in the Lyman series of the hydrogen spectrum (in $\text{ nm}$)? (Take $hc = 1240 \text{ eV nm}$)

In hydrogen atom spectra,if the ratio of wavelengths corresponding to the first line of the Lyman series and the first line of the Balmer series is $9 \alpha$,the value of $\alpha$ is