Which of the following elements forms a most stable ion with a charge of +2?

• A. Cl
• B. Na
• C. Al
• D. Mg

Answer: (D)

Verified step by step guidance

1. Identify the elements given in the problem and their typical ionic charges: Cl (chlorine) usually forms a -1 ion, Na (sodium) forms a +1 ion, and Al (aluminum) forms a +3 ion.
2. Recall that the problem asks which element forms the most stable ion with a charge of +2, so check if each element can commonly form a +2 ion and how stable that ion is.
3. Consider the electron configurations of each element and how losing two electrons affects their stability. For example, losing two electrons to achieve a noble gas configuration is often very stable.
4. Recognize that magnesium (Mg), although not listed in the options, commonly forms a +2 ion by losing two electrons to achieve a stable noble gas configuration, which explains why Mg^{2+} is very stable.
5. Conclude that among the given elements, none typically form a +2 ion as stable as Mg^{2+}, which is why Mg is the correct answer for forming the most stable +2 ion.