The figure indicates the energy level diagram of an atom and the origin of six spectral lines in emission (e.g.,line no. $5$ arises from the transition from level $B$ to $A$). Which of the following spectral lines will also occur in the absorption spectrum?

Let $T_{1}$ and $T_{2}$ be the energy of an electron in the first and second excited states of a hydrogen atom,respectively. According to the Bohr's model of an atom,the ratio $T_{1}: T_{2}$ is

An electron of a hydrogen-like atom,having $Z=4$,jumps from the $4^{\text{th}}$ energy state to the $2^{\text{nd}}$ energy state. The energy released in this process will be $......... \text{eV}$.
(Given $Rch = 13.6 \text{ eV}$)
Where $R =$ Rydberg constant,
$c =$ Speed of light in vacuum,
$h =$ Planck's constant.

If an electron in the excited state falls to the ground state,a photon of energy $5 \ eV$ is emitted. The wavelength of the photon is nearly: (in $nm$)

$A$ $12.5 \ eV$ electron beam is used to bombard gaseous hydrogen at room temperature. It will emit:

What is the ground state of an atom? And what is the ionization energy and excitation energy of a hydrogen atom?