GKFix MCQ Question

What is the expression for the second ionization constant (Ka2) of a dibasic acid HX–?

• A. Ka2 = [H+][X^2–]/[HX–]
• B. Ka2 = [H+][HX–]/[H2X]
• C. Ka2 = [H+][X^2–]/[H2X]
• D. Ka2 = [H+][H2X]/[HX–]