Answer: B. Have eight electrons in their outer shell.
Step-by-step explanation:
Noble gases are known for their unreactive nature due to the presence of complete outermost electron. They possess eight electrons in their outermost shell (octet rule). Being unreactive means that they cannot share any of their outermost electron to any other atoms since they are completely filled up (stable).
Taking sodium(2 8 1) which is reactive as an example, its reactivity is due to the presence of a lone pair of electron in its outermost shell which it can easily share to other atom with incomplete outermost electron like chlorine (2 8 7).