In the Bohr model of the hydrogen atom,the lowest orbit corresponds to:

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

The four lowest energy levels of an $H$-atom are shown in the figure. The number of possible emission lines would be

As an electron makes a transition from an excited state to the ground state of a hydrogen-like atom/ion:

The electron in a hydrogen atom first jumps from the third excited state to the second excited state and subsequently to the first excited state. The ratio of the respective wavelengths,$\lambda_1/\lambda_2$,of the photons emitted in this process is

The energy (in $eV$) required to excite an electron from $n=2$ to $n=4$ state in a hydrogen atom is: