If an electron is moving in the $n^{th}$ orbit around the nucleus with a velocity $v$ and radius $r$,then the value of $n$ is .........

Angular momentum of an electron in the second shell of a $Li^{+2}$ ion is:

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:

$A$ certain electronic transition from an excited state to the ground state of the $H$ atom in one or more steps gives rise to four lines in the ultraviolet region of the spectrum. How many lines does this transition produce in the infrared region of the spectrum?

When an electron makes a transition from $(n+1)$ state to $n^{th}$ state,the frequency of emitted radiation is related to $n$ according to $(n >> 1)$:

If the wavelength of the limiting line of the Lyman series of the hydrogen atom is $16$ times the wavelength of the limiting line of the same series for an ion $X$,then what is $X$?