Which of the following elements is least likely to form an ion?

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

Answer: (A)

Verified step by step guidance

1. Step 1: Understand what it means for an element to form an ion. Elements form ions by either losing or gaining electrons to achieve a stable electron configuration, often resembling the nearest noble gas configuration.
2. Step 2: Identify the electron configurations of the given elements: Sodium (Na), Magnesium (Mg), Chlorine (Cl), and Neon (Ne). Neon is a noble gas with a full outer shell, while the others have incomplete outer shells.
3. Step 3: Recognize that elements with full outer electron shells (like Neon) are very stable and have little tendency to gain or lose electrons, making them unlikely to form ions.
4. Step 4: Compare the other elements: Sodium and Magnesium tend to lose electrons to form positive ions, and Chlorine tends to gain electrons to form negative ions.
5. Step 5: Conclude that Neon, having a complete octet and being chemically inert, is the least likely to form an ion among the options.