What are energy levels or shells ?

What is Fermi energy level ?

What are trophic levels?

When a nucleus in an atom undergoes a radioactive decay, the electronic energy levels of the atom.

The simple Bohr model cannot be directly applied to calculate the energy levels of an atom with many electrons. This is because

Calculate the ratio of energies of photons produced due to transition of electron of hydrogen atom from its, Second permitted energy level to the first level? 2. The highest permitted energy levels to first permitted level?