n |
l |
m |
m |

2 |
1 |
0 |
X |

n |
l |
m |
m |

2 |
1 |
0 |
Y |

If the above quantum numbers describe two different electrons in a fluorine atom, and the magnetic spin number X is +1/2, what is the magnetic spin number of Y?

The Pauli Exclusion Principle states that no two electrons can have the same four quantum numbers. Therefore, if X = +1/2, then the second electron must spin in the opposite direction (Y = -1/2).