The energy in nth orbit of Hydrogen atom is 13.6/n2.
In 1st orbit=> E=13.6 eV
In 2nd orbit, E=3.4 eV
In 3rd orbit, E=1.5 eV
Here E1-E2 = 10.2 eV AND E2-E3 = 1.9 eV
THe difference in energy level further goes on decreasing.
So energy difference is maximum between 1st and 2nd level