The total energy of an electron in the $n^{th}$ stationary orbit of the hydrogen atom can be obtained by

An electron in a stationary hydrogen atom jumps from the $4^{\text{th}}$ energy level to the ground level. The velocity that the photon acquired as a result of the electron transition will be ($h=$ Planck's constant,$R=$ Rydberg's constant,$m=$ mass of the photon).

The energy required to remove an electron from the first excited state of $Li^{++}$ is ......... $eV$.

Assertion : Between any two given energy levels,the number of absorption transitions is always less than the number of emission transitions.
Reason : Absorption transitions start from the lowest energy level only and may end at any higher energy level. But emission transitions may start from any higher energy level and end at any energy level below it.

During the transition of an electron from state $A$ to state $C$ of a Bohr atom,the wavelength of the emitted radiation is $2000 \ \mathring A$ and it becomes $6000 \ \mathring A$ when the electron jumps from state $B$ to state $C.$ Then the wavelength of the radiation emitted during the transition of electrons from state $A$ to state $B$ is