What hydrogen atom transitions represent emission of the longest wavelength photon?

Wavelength has inverse relationship with its energy. The shorter the wavelength, the higher the energy.

Complete question was:
Which of the following transitions (in a hydrogen atom) represent emission of the longest wavelength photon?n = 1 to n = 2 n = 3 to n = 1 
n = 3 to n = 4 
n = 4 to n = 2 
n = 5 to n = 4

The longest wavelength photon is n = 5 to n = 4. As I stated above,the wavelength and energy has inverse relationship. The longest wavelength has the lowest energy.

It was ernest rutherford