A 1000-ML Sample of 0 $\times$ 10^-10
B)4 $\times$ 10^-5
D)not Enough Information to Calculate
E)none of These

Multiple Choice

A 100.0-mL sample of 0.503 M H₂A (diprotic acid) is titrated with 0.200 M NaOH.After 125.0 mL of 0.200 M NaOH has been added,the pH of the solution is 4.50.Calculate K_a1 for H₂A.

A) 3.2 $\times$ 10^-10
B) 4.5
C) 3.1 $\times$ 10^-5
D) not enough information to calculate
E) none of these