Final answer:
The force between two charged dust particles can either be attraction or repulsion and is governed by Coulomb's law; however, without knowing the specific charges of the particles, the nature of the force is not specified.
Step-by-step explanation:
When two charged dust particles are in proximity, they exert a force on each other. This can either be a force of attraction or repulsion, depending on the nature of their charges. According to Coulomb's law, like charges repel each other, while opposite charges attract. So, if both particles have the same type of charge, they will repel each other. However, if one particle has a positive charge and the other has a negative charge, they will be attracted to each other.
The force acts along the line joining the centers of the two charges. For example, if two positively charged dust particles are present, the electrostatic force between them would be repulsive. Conversely, if one particle is positively charged and the other negatively charged, they will attract each other. This principle is central to understanding not only the behavior of charged particles but also real-world phenomena such as why dust sticks to a computer screen (because the dust becomes polarized and is attracted to the screen).
Therefore, when considering the nature of the force between two charged dust particles, all the described scenarios are plausible. But, to mention the correct option in the final answer, we need to know the charges of the dust particles. As the information provided is not specified, the answer to the question is (d) Not specified.