Which of the following best describes the noble gases?

have an outer electron shell that needs only 1 electron

are highly reactive

have a full outer electron shell

combine easily with other elements

Answer: third option: have a full outer electron shell.

Explanation:

Noble gases is the family name given to the elements of group 18 of the periodic table.

The electron valence shell of all these elements is full:

He has two electrons wich is the maximum an atom of the first row can have.

Ne, Ar, Kr, Xe, and Rn (well you can include Og which is the last noble gas discovered; it is the element number 118), have 8 electrons on their valence electron shell, which is the maximum any element can have.

Precisely, that feature (valence shell full) accounts for the low reactivity of these elements, which conferred them the title of nobles (they hardly combine with other elements to form compounds).