Which of the transitions in a hydrogen atom emits a photon of the lowest frequency? ($n =$ quantum number)

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

When a hydrogen atom is raised from the ground state to an excited state,

Energy levels $A, B$ and $C$ of a certain atom correspond to increasing values of energy, i.e., $E_A < E_B < E_C$. If $\lambda_1, \lambda_2$ and $\lambda_3$ are the wavelengths of radiations corresponding to transitions $C$ to $B, B$ to $A$ and $C$ to $A$ respectively, which of the following relations is correct?

An electron in a hydrogen atom makes a transition from the $(n+1)^{th}$ orbit to the $n^{th}$ orbit. For large $n$,the wavelength of the emitted radiation is proportional to:

The energy required to remove an electron in a hydrogen atom from $n = 10$ state is (in $\text{ eV}$)