Which of the following phenomena suggests the presence of electron energy levels in atoms?

If the binding energy of the electron in a hydrogen atom is $13.6 \ eV$,then the energy required to remove the electron from the first excited state of $Li^{2+}$ is: (in $eV$)

The first excited state of a hydrogen atom is $10.2 \ eV$ above the ground state. What temperature is needed to excite a hydrogen atom to its first excited state?

An electron with kinetic energy $E$ collides with a hydrogen atom in the ground state. The collision will be elastic

Which of the following transitions in hydrogen atoms emit photons of highest frequency?

$A$ hydrogen atom falls from $n^{\text{th}}$ higher energy orbit to the first energy orbit $(n=1)$. The energy released is equal to $12.75 \text{ eV}$. The $n^{\text{th}}$ orbit is: