The diagrams below show the different stages of titration for a weak diprotic acid H₂X(aq) with KOH(aq). For simplicity, water molecules and K⁺ ions are not shown. Identify the solution that has the highest pH and the solution that has the lowest pH.

• A. Highest pH: Solution (ii); Lowest pH: solution (iv)
• B. Highest pH: Solution (i); Lowest pH: solution (iii)
• C. Highest pH: Solution (iii); Lowest pH: solution (i)
• D. Highest pH: Solution (iv); Lowest pH: solution (ii)

Answer: (B)