Question

multiple choice question
group 18 elements are unreactive because
o their electrons are held particularly strongly by their nucleus.
o they are relatively massive compared with other elements
o they have complete outer energy levels

Explanation:

Group 18 elements (noble gases) are unreactive because they have a full outer - shell of electrons (complete outer energy levels). This stable electron configuration means they do not easily gain, lose, or share electrons to form chemical bonds. The fact that their electrons are held strongly by the nucleus is not the main reason for their unreactivity (as some other elements also have electrons held strongly but are reactive). Their mass (compared to other elements) has no direct relation to their chemical reactivity.

Answer:

they have complete outer energy levels