Two series of spectral lines of atomic hydrogen which do not belong to the infrared spectral region are

In the Bohr series of lines of the hydrogen spectrum,the third line from the red end corresponds to which one of the following inter-orbit jumps of the electron for Bohr orbits in an atom of hydrogen?

The difference in radii between the fourth and third Bohr orbits of $He^{+}$ (in $m$) is:

If an electron transitions from $n = 5$ to $n = 2$ in a hydrogen spectrum,identify the series and the region of the spectrum.

In a hydrogen atom,the minimum energy required to excite an electron from the $2^{nd}$ orbit to the $3^{rd}$ orbit is: (in $eV$)

The ratio of the slopes of the $KE_{max}$ vs $v$ and $V_0$ vs $v$ curves in the photoelectric effect gives ($v$ is the frequency of incident radiation and $V_0$ is the stopping potential).