$HB$ has the largest $K_a$.
Work Step by Step
1. $K_a$ is proportional to ionization. The larger the $K_a$, the greater is the ionization. - Therefore, the acid that produces mores $H^+$ and its conjugate base (greatest ionization) is the one with the largest $K_a$ 2. Count the amount of protons in each image. $HA$: 1 proton $HB$: 4 protons $HC$: 2 protons - Since HB has more protons, it is the one with the largest $K_a$.