Answer
It should jump to the state $n = 3$
Work Step by Step
In the ground state state, $n = 1$
When the electron is in the third excited state, then $n = 4$
To emit light, the electron must jump down to a lower state where $n \lt 4$
Note that light with a longer wavelength has less energy than light with a shorter wavelength.
To emit light with the longest possible wavelength, the electron must jump down to the state that is one step lower so that the energy difference between states is a minimum.
It should jump to the state $n = 3$
