The minimum excitation energy of an electron revolving in the first orbit of hydrogen is (in $eV$)

The energy required to excite an electron from the ground state of a hydrogen atom to the first excited state is:

An electron of a stationary hydrogen atom transits from the fourth energy level to the ground level. The velocity of the hydrogen atom acquired as a result of photon emission will be:
{ $R =$ Rydberg constant,$m =$ mass of hydrogen atom }

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?

What is the ratio of the total energy of an electron in a hydrogen atom in the first excited state to that in the third excited state?

The total energy of an electron in an orbit of a hydrogen atom is $E$. The potential energy of the electron in the same orbit is: