When an electron in a hydrogen spectrum transitions from the $7^{th}$ energy level to the $1^{st}$ energy level,what is the total number of spectral lines produced?

The ratio of the radius of the second orbit of hydrogen to the third orbit of $Li^{+2}$ is .... ($H$ atomic number = $1, Li$ atomic number = $3$)

If the radius of the $3^{\text{rd}}$ Bohr's orbit of hydrogen atom is $r_{3}$ and the radius of $4^{\text{th}}$ Bohr's orbit is $r_{4}$,then which of the following relations is correct?

What is the wavelength of light required to raise an electron in the $O^{7+}$ ion from $n=1$ shell to $n=2$ shell in $nm$?

The ionization energy of a hydrogen atom is $13.6 \ eV$. The energy required to ionize a hydrogen atom in its second excited state is ........... $eV$.

The series limit for the Balmer series of $H$ atom spectra is: