The correct option is **C. Electrostatic forces act between charged particles, while gravitational forces act between masses.** ### Detailed Explanation: 1. **Understanding Electrostatic Forces:** - Electrostatic forces arise from the interaction between charged particles. These charges can be positive or negative, and the force can be either attractive (between opposite charges) or repulsive (between like charges). The strength of the electrostatic force is described by Coulomb's Law, which states that the force \( F \) between two point charges \( q_1 \) and \( q_2 \) separated by a distance \( r \) is given by: \[ F = k \frac{|q_1 q_2|}{r^2} \] where \( k \) is Coulomb's constant (\( 8.99 \times 10^9 \, \text{N m}^2/\text{C}^2 \)). 2. **Understanding Gravitational Forces:** - Gravitational forces, on the other hand, act between masses. According to Newton's Law of Universal Gravitation, the force \( F \) between two masses \( m_1 \) and \( m_2 \) separated by a distance \( r \) is given by: \[ F = G \frac{m_1 m_2}{r^2} \] where \( G \) is the gravitational constant (\( 6.674 \times 10^{-11} \, \text{N m}^2/\text{kg}^2 \)). Unlike electrostatic forces, gravitational forces are always attractive. 3. **Why Option C is Correct:** - Option C accurately states that electrostatic forces act between charged particles, while gravitational forces act between masses. This distinction is fundamental to understanding the nature of these two types of forces. Electrostatic forces can vary in direction (attractive or repulsive), while gravitational forces are always attractive. ### Why the Other Options are Incorrect: - **Option A: Electrostatic forces are always attractive, while gravitational forces can be both attractive and repulsive.** - This statement is incorrect because electrostatic forces can be both attractive (between opposite charges) and repulsive (between like charges). Gravitational forces, however, are always attractive. - **Option B: Gravitational forces are significantly stronger than electrostatic forces at atomic scales.** - This statement is misleading. In fact, electrostatic forces are much stronger than gravitational forces at atomic scales. For example, the electrostatic force between two protons is about \( 10^{36} \) times stronger than the gravitational force between them. Thus, this option is incorrect. - **Option D: Both electrostatic and gravitational forces obey the inverse square law but only gravitational forces can be shielded.** - This statement is partially correct in that both forces do obey the inverse square law. However, it is incorrect to say that only gravitational forces can be shielded. Electrostatic forces can also be shielded by materials that block electric fields, such as conductive materials. Therefore, this option is misleading. ### Summary of Key Points: - **Electrostatic forces** act between charged particles and can be attractive or repulsive. - **Gravitational forces** act between masses and are always attractive. - **Coulomb's Law** and **Newton's Law of Universal Gravitation** describe the respective forces. - At atomic scales, **electrostatic forces** are significantly stronger than gravitational forces. This understanding is crucial for distinguishing between these two fundamental forces in physics.