Answer
Protein B will have higher affinity for the ligand X.
$K_{d}$ of protein B for ligand X is lower than protein A.
$K_{a}$ for protein A is $10^{6} M^-{1} $ and for B it is $10^{9} M^-{1}$
Work Step by Step
$K_{a}$ is the inverse of $K_{d}$.
