Final answer:
The most stable and nonreactive atoms are ones that have full energy levels, typically found in the noble gases such as helium, neon, and argon, due to their full valence shell satisfying the octet rule.
Step-by-step explanation:
The most stable atoms, and thus those that are typically nonreactive, are the atoms that have full energy levels. These configurations occur in the noble gases such as helium, neon, argon, etc., which have completely filled valence shells. The full valence shell configuration makes an atom particularly stable since it has a settled arrangement of electrons that satisfy the octet rule. This rule suggests that most atoms strive to have eight electrons in their outer shell to achieve maximum stability. Considering chemical behavior, atoms with full valence shells (the noble gases) tend not to engage in chemical reactions because they have no need to gain or lose electrons to reach a stable configuration.