Which of the following corresponds to the energy of a possible excited state of hydrogen (in $eV$)?

For $Li^{2+}$,the ratio of radii $r_2 : r_5$ is:

The radius of the second orbit of a hydrogen atom is the same as that of orbit $n$ of an ion $x$. $n$ and $x$ are respectively:

An excited hydrogen atom emits light in the ultraviolet region at a frequency of $2.47 \times 10^{15} \ Hz$. Calculate the energy of a single photon. (Given: $h = 6.63 \times 10^{-34} \ J \cdot s$)

The total energy of the electron in the hydrogen atom in the ground state is $-13.6 \, eV$. What is the stopping potential in volts required to remove this electron from the ground state?

What is the radius ratio for the $2^{nd}$ orbit of $Li^{+2}$ ion to the $3^{rd}$ orbit of $Be^{+3}$ ion?