Identifying Period 2 element forming MgX₂ ionic compound

Steps:

• Period 2 elements include Li to Ne; among choices, fluorine (F) and oxygen (O) are in Period 2, while chlorine (Cl) and sulfur (S) are in Period 3.
• The formula MgX₂ shows magnesium (+2 charge) bonds with two X ions, so X must have -1 charge.
• Halogens like fluorine gain one electron to form -1 ions, producing MgF₂.
• Oxygen gains two electrons to form O²⁻, resulting in MgO, not MgO₂.

Why B is correct:

• Fluorine, a Period 2 halogen, forms F⁻ ions, yielding the ionic compound MgF₂ per the octet rule.

Why the others are wrong:

• A. Chlorine is in Period 3, not 2.
• C. Oxygen forms O²⁻ ions, giving MgO instead of MgO₂.
• D. Sulfur is in Period 3 and forms S²⁻ ions, giving MgS.

Final answer: B