Pauli's exclusion principle is a rule that determines the restriction on the number of electrons that can occupy a specific atomic orbital. According to this principle: No two electrons in an atom can have the same values for the four quantum numbers.
For a given atomic orbital (e.g., 1s, 2s, ...), the value of the principal, angular momentum, and magnetic quantum numbers are the same. So it can accommodate two electrons, provided the electrons have opposite spin.
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