Which of the following compounds contains a metal ion that can both accept and donate electrons (i.e., exhibits variable oxidation states)?

• A. MgO
• B. FeCl3
• C. NaCl
• D. KBr

Answer: (B)

Verified step by step guidance

1. Understand the concept of variable oxidation states: A metal ion that can both accept and donate electrons exhibits multiple oxidation states, meaning it can exist in more than one positive charge state in different compounds.
2. Examine each compound and identify the metal ion present: MgO contains Mg²⁺, FeCl₃ contains Fe³⁺, NaCl contains Na⁺, and KBr contains K⁺.
3. Recall the common oxidation states of these metal ions: Magnesium (Mg) typically has only one stable oxidation state, +2; Sodium (Na) and Potassium (K) also have a single common oxidation state, +1.
4. Recognize that Iron (Fe) is a transition metal known for variable oxidation states, commonly +2 and +3, which means it can both accept and donate electrons in different chemical environments.
5. Conclude that FeCl₃ contains the metal ion (Fe) that exhibits variable oxidation states, making it the correct answer.