Task: Text Categorization
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:  <0> one. <1> 3. <2> 5. <3> 7 <4> 9
Output (English): chemistry