An electron in a hydrogen atom in its ground state absorbs $2$ times as much energy as the minimum required for it to escape from the atom. The kinetic energy of the emitted electron is ............ $eV$.

Calculate the radius of the fourth orbit of the $B^{4+}$ ion. (in $pm$)

The ratio of the radius of the $2^{nd}$ orbit of $H$ to the radius of the $3^{rd}$ orbit of $He^{+}$ is ......

How many photons are required to provide $1 \, J$ of energy with a wavelength of $5000 \, \mathring{A}$?

Consider the following spectral lines for atomic hydrogen:
$A$. First line of Paschen series
$B$. Second line of Balmer series
$C$. Third line of Paschen series
$D$. Fourth line of Bracket series
The correct arrangement of the above lines in ascending order of energy is:

What is the shortest wavelength for the Paschen series of the $Li^{2+}$ ion?