Task: Question Answering
Input (English): Question: If we value 25 mL of an H2A acid in concentration 0.1000M (pKa1 = 5, pKa2 = 9) with NaOH, the pH when we have evaluated 50% of the initial acid will be: 
 Options:  <1> one. <2> 3. <3> 5. <4> 7 <5> 9
Output (English): 3