The frequency of radiation absorbed or emitted when transition occurs between two stationary states with energies `E_(1)` (lower) and `E_(2)` (higher) is given by
A. `v=(E_(1)+E_(2))/h`
B. `v=(E_(1)-E_(2))/h`
C. `v=(E_(1)xxE_(2))/h`
D. `v=(E_(2)-E_(1))/h`