Final answer:
Noble gases like helium, neon, and argon have a filled outer electron shell according to the octet rule, which along with their nonmetallic nature, makes them unreactive.
Step-by-step explanation:
All noble gases (helium, neon, argon, etc.) have in common a filled outer electron shell, which makes them exceptionally stable and nonreactive. This configuration is often described using the octet rule, where atoms tend to be energetically favorable when they possess eight electrons in their valence shell. For noble gases, the combination of having a full outer electron shell and being nonmetals contributes to their lack of reactivity. Therefore, the correct answer to what they have in common and why they don't react with other elements is a. They have a full outer electron shell; They are nonmetals.