In the gravitational force law $F = G\dfrac{m_1 m_2}{d^2}$, the quantity $G$ is best described as:

1. In the equation $F = G\dfrac{m_1 m_2}{d^2}$, $G$ is the constant of proportionality. 2. It is called the universal gravitational constant. 3. It numerically equals the gravitational force between two 1 kg masses kept 1 m apart. 4. It is distinct from $g$ (acceleration due to gravity), so the acceleration option is wrong. _Source: Balbharati (Maharashtra Board) Class 10 Science & Technology, Ch 1 "Gravitation", p.13_