Why distance of electrons from the nucleus is the same for same element?
In atomic scale physicists normally do not talk about "distance" unless in practical context. Electron's presence around the nucleus is described by its wavefunction which is a function of space. By distance, you must mean the most probable distance to find an electron in a particular state from the nucleus. This quantity is state/wavefunction dependent, and what determines the eigenstate of an atom is its associated Schroedinger equation. The most probable distance to find an electron need not necessarily the same for same element, again it depends on the state of that atomic element at that instant of time. only when two identical elements are exactly in the same state, will you find the electron's most probable position exactly the same.
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