The dissociation constant Kd for ligand binding to the receptor is 10⁻⁷ M. The concentration of ligand required for occupying 10% of receptors is (A) 10⁻⁶ M (B) 10⁻⁷ M (C) 10⁻⁸ M (D) 10⁻⁹ M

Answer: (B) 10⁻⁷ M
The dissociation constant Kd represents the concentration of ligand at which 50% of receptors are occupied. For 10% occupancy, the concentration is close to Kd, which is 10⁻⁷ M.