The question asks to identify the correct statement regarding gravitational force.
Let's examine each statement:
This is incorrect. Gravitational force acts universally and does not depend on the medium separating the masses. For instance, the gravitational pull between Earth and the Moon is not altered by the presence of air or vacuum.
This is incorrect. Gravitational force is dependent on the mass of the objects, not their electric charge. Electric force depends on charge, but gravitational force does not.
This is incorrect. Unlike electric or magnetic forces, gravitational force only exerts an attraction between objects with mass. There is no known repulsive gravitational force.
This is correct. The fundamental characteristic of gravitational force, as described by Newton's Law of Universal Gravitation (F = G \frac{m_1 m_2}{r^2}), is that it always pulls objects towards each other. The force is always positive, indicating attraction.
Based on the analysis, the only correct statement describing gravitational force is that it is always attractive.