From A to C, Energy=12400/3000=4.13 eV From B to C, Energy=12400/6000=2.1eV Now, if we subtract the second equation from the first, we`ll get the energy of the electron when it jumps from A to B. So, Energy=4.13-2.1 eV =2.03 ≈2eV Therefore, Wavelength= 12400/2 Angstorm =(around 6000 Angstorm)