Hi, thank you for posting your question here at Brainly.
The acid dissociation constant, Ka, is an equilibrium constant that measure the strength of an acid. It is a ratio of the concentration of the products (salt and water) and the reactants (acid). The higher the Ka, the more tendency it is to favor the product side, which means more tendency to donate H+ ions. This is exactly the definition of a strong acid (high H+ ionized).
Thus, the answer is letter D.
The atomic radius increases as you go down a group.
