The correct answer is D) zero. When a ship is inclined to an angle of list, the righting arm is zero. This is because the center of gravity and the center of buoyancy are aligned vertically, resulting in no righting moment or righting arm. The ship is in a state of equilibrium, and there are no forces acting to restore the ship to an upright position. The other answer choices are incorrect because: A) a positive righting arm would indicate the ship is trying to return to an upright position, which is not the case when the ship is inclined at an angle of list; B) the maximum righting arm occurs at small angles of heel, not at the angle of list; and C) a negative righting arm would indicate the ship is being pushed further over, which is also not the case at the angle of list.