GKFix MCQ Question

What is the expression for Ka1 of a diprotic acid H2A?

• A. Ka1 = [H+][A2–]/[HA–]
• B. Ka1 = [HA–]/[H2A]
• C. Ka1 = [H+]^2/[H2A]
• D. Ka1 = [H+][HA–]/[H2A]