What is aufbau principal , hund rule , pauli rule

1.	What is aufbau principal , hund rule , pauli rule
Answer» Aufbau principle : the electrons are filled in the orbital according to their increasing order of energyHund rule : no pairing of electrons can take place until and unless each of the orbital is singly occupiedPauli rule : no two electrons can have same set of four quantum numbers or two electrons in an orbital must different spins to attain stability in an atom where one electron revolves anti clockwise and the other clockwise or vice versa with charge +1/2 or -1/2 or vice versa accordingly

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