They have a full valence shell (8 electrons in the outer shell) so they are the most stable elements on the periodic table. Therefore, they do not need to react to other elements to gain or lose elections to become stable.
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Answer:
I think the answer is the 3rd one
<span>For isotopes of any element, the number of protons remains the same, BUT the number of neutrons changes. Since each of the isotopes listed is phosphorus, All three have 15 protons. (They have 16, 17 and 18 protons respectively.)</span>
