The first line in the Lyman series has wavelength $\lambda $. The wavlength of the first line in Balmer series is

The wavelength of the first line of Balmer series of hydrogen atom is $\lambda \,\mathop A\limits^o $. The wavelength of this line of a double ionised lithium atom $(Z = 3)$is

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

An $X-$ ray tube is operated at $50\, kV$. the minimum wavelength produced is…….$\mathop A\limits^o $

Hydrogen atom is excited from ground state to another state with principal quantum number equal to $4$. Then the number of spectral lines in the emission spectra will be