GKFix MCQ Question

Why is the ionisation enthalpy of Fe2+ lower than that of Mn2+ according to the text?

• A. Fe2+ has a d6 configuration while Mn2+ has a d5 configuration, making Fe2+ easier to ionise
• B. Mn2+ has a more stable configuration than Fe2+
• C. Fe2+ has a higher nuclear charge
• D. Mn2+ has a lower effective nuclear charge