Titration curve for weak acid-strong base

Steps:

• Initial pH is higher than strong acid due to partial dissociation of weak acid.
• In buffer region (before equivalence), pH rises gradually as conjugate base forms, following Henderson-Hasselbalch equation.
• At equivalence point, pH >7 from salt hydrolysis; steep rise occurs here.
• After equivalence, excess strong base causes rapid pH increase, then levels off.

Why D is correct:

• D matches the weak acid-strong base curve: initial pH 3-4, buffer plateau near pKa, equivalence pH ~9, per titration theory.

Why the others are wrong:

• A shows strong acid curve: starts at pH ~1, no buffer region.
• B depicts strong acid-strong base: symmetric steep rise at equivalence, pH=7.
• C resembles weak base-strong acid: starts high pH, equivalence <7.

Final answer: D