The correct answer is option 4: "The quantity G is a universal constant."

Let`s break down each option to better understand why option 4 is the correct answer.

Option 1 states that the quantity G depends on the local value of acceleration due to gravity. However, this statement is incorrect. The quantity G, also known as the gravitational constant, is a fundamental constant in physics and does not depend on the local value of acceleration due to gravity.

Option 2 states that the quantity G is greatest at the surface of the Earth. This statement is also incorrect. The value of G remains constant throughout the universe and is not specifically influenced by the surface of the Earth.

Option 3 states that the quantity G is used only when Earth is one of the two masses. This statement is not true. The gravitational constant G is used to calculate the force of gravity between any two masses in the universe, not just when one of them is the Earth.

Option 4 is the correct answer because the quantity G is indeed a universal constant. It is a fundamental constant that appears in the equation for gravitational force and remains the same regardless of the location or masses involved.