Which of the following best explains why noble gases are the least reactive elements on the periodic table?

• A. They have the lowest ionization energies, allowing them to easily lose electrons.
• B. They have the highest metallic character among all elements.
• C. They have the largest atomic radii, which prevents them from reacting.
• D. They have completely filled valence electron shells, making them chemically stable.

Answer: (D)

Verified step by step guidance

1. Understand that chemical reactivity is largely determined by the electron configuration of an element, especially the electrons in the outermost shell (valence electrons).
2. Recall that noble gases have a unique electron configuration where their valence shells are completely filled with electrons, which is a very stable arrangement.
3. Recognize that elements tend to react in order to achieve a full valence shell, either by losing, gaining, or sharing electrons to reach a stable electron configuration similar to noble gases.
4. Analyze the given options: low ionization energy would make an element more reactive, high metallic character is not characteristic of noble gases, and large atomic radii do not directly cause low reactivity.
5. Conclude that the best explanation for the low reactivity of noble gases is their completely filled valence electron shells, which make them chemically stable and unlikely to participate in reactions.