Which of the following elements is least likely to undergo a chemical reaction?

• A. Neon (Ne)
• B. Chlorine (Cl)
• C. Magnesium (Mg)
• D. Sodium (Na)

Answer: (A)

Verified step by step guidance

1. Understand that the likelihood of an element undergoing a chemical reaction depends on its electron configuration, particularly its valence electrons.
2. Recall that elements tend to react to achieve a full valence shell, often resembling the electron configuration of the nearest noble gas.
3. Identify that Neon (Ne) is a noble gas with a complete octet (full valence shell), making it very stable and unlikely to react chemically.
4. Compare Neon with Chlorine (Cl), Magnesium (Mg), and Sodium (Na), which all have incomplete valence shells and tend to react to achieve stability.
5. Conclude that Neon (Ne), having a full valence shell and high stability, is the least likely to undergo a chemical reaction.