Which of the following weakest ?

Question

$\begin{array}{1 1} (a)\;C_6H_5NH_2:K_b=3.8 \times 10^{-10} \\ (b)\;C_6H_5NH_2:K_b=4.8 \times 10^{-10} \\ (c)\;C_6H_5NH_2:K_b=5.8 \times 10^{-10}\\ (d)\;C_6H_5NH_2:K_b=6.8 \times 10^{-10} \end{array}$