a 103 M solution of this acid?

A . 3.0

B . 4.7 ---correct ans

C . 6.3

D . 9.3

Ka will be 10^-6.4 and thus Ka = (HCO3-)(H+)/ (H2CO3)

10^-6.4 = x2/ 10^-3

x2 = 10^9.4

x approximately equal to 3, infact a little less than 3.

Can anyone please solve this problem. I don't understand the Kaplan explanation. They said that the ka = 4*10^-7