In Bohr series of lines of 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
As we have learnt,
Balmer series of Hydrogen spectrum lies in the visible region.
Therefore, the transition corresponding to the least energy or largest wavelength is n=3 to n=2 which corresponds to red colour
So, the third line from red end will be of the transition from n=5 to n=2