The energy of de-excitation I am 10th class student and what i dont get is when electron dexcites it produces energy but what is main phenomenon which produces energy is it the motion of electron or something like disturbing field which produces energy.
 A: De-exictation is the process of transitioning from a high energy state to a lower energy state; the photon emitted has energy equal to the difference in the energy of the two states.
If we're tacitly assuming that we started with a system in the ground (i.e. lowest energy) state, then something had to put the electron into the higher energy state before we could even consider the possibility of de-excitation (which is to say it had to be excited first).
If the question was "where did the energy that the photon got come from originally?", the answer is the energy came from whatever it was the excited the electron.
If the question was "How was the energy stored in the excited state?" the answer is as a combination of electric potential energy between the electron and nucleus and kinetic energy (mostly of the electron, but to a small degree also of the nucleus). 
But that combination is subject to uncertainty: the electron doesn't have a well defined distance from the nucleus so the system doesn't have a well defined electric potential energy and neither does the electron have a well defined momentum meaning that it's kinetic energy is likewise not well defined. All you can say for sure is that the state has a well defined energy (actually, because it is unstable and will decay even the total energy is subject to a small uncertainty, but for most purposes that is negligible).
