The electrostatic force of attraction between the electron and the nucleus in a hydrogen atom is given by:

The wavelength and frequency of a photon with energy $2 \ eV$ are respectively:

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 energy of an electron in the first Bohr orbit of the hydrogen atom is $-13.6 \ eV$. Calculate the energy of an electron in the first Bohr orbit of $He^{+}$ in $eV$.

According to Bohr's theory,
$E_{n} = \text{Total energy}, K_{n} = \text{Kinetic energy}, V_{n} = \text{Potential energy}, r_{n} = \text{Radius of } n^{\text{th}} \text{ orbit}$
Match the following:

Column $I$	Column $II$
$A$. $V_{n} / K_{n} = ?$	$P$. $0$
$B$. If radius of $n^{\text{th}}$ orbit $\propto E_{n}^{x}, x = ?$	$Q$. $-1$
$C$. Angular momentum in lowest orbital	$R$. $-2$
$D$. $1/r_{n} \propto Z^{y}, y = ?$	$S$. $1$

The radius of the first Bohr's orbit of the hydrogen atom is ............. $\mathring{A}$.