Concept:The noble gases are unreactive because their outermost electron shells are completely filled.
Explanation:Group VIII elements include helium, neon, argon, krypton, xenon, and radon.
These elements are called inert gases because they do not readily take part in chemical reactions.
A completely filled valence shell makes them electronically stable.
Since the valence shell is full, they have no tendency to gain, lose, or share electrons.
Therefore, they exist as stable single atoms and show very low reactivity.
Answer:B. They all have completely filled valence shells.