Answer:
Options A and B
Step-by-step explanation:
The Pauli Exclusion Principle states that, in an atom or molecule, no two electrons can have the same four electronic quantum numbers. As an orbital can contain a maximum of only two electrons, the two electrons must have opposing spins.
Going through the options;
Option A - An electron shell can have more than two electrons. An orbital however can hold a maximum of two electrons.
Option B - This is correct because No two electrons in a atom can have the same four quantum numbers . This means that only two electrons are allowed in the same orbital, and then they have opposite spin, +1/2 and -1/2.
Option C - Each electron orbital (state) can only contain a maximum of two lectrons.
Option D - This is wrong because no two electrons in a atom can have the same four quantum numbers . This means that only two electrons are allowed in the same orbital, and then they must have opposite spin, +1/2 and -1/2.