Final answer:
Electrostatic precipitators utilize rappers to remove the collected dust from the electrodes by vibrating and dislodging the particles.
Step-by-step explanation:
Electrostatic precipitators use rappers to remove the dust from the collecting electrodes. These devices, integral to air pollution control, implement a two-stage process. In the first stage, air is passed through grids of opposite charge where airborne particles become charged. Then, in the second stage, the now-charged particles are attracted to and collected on oppositely charged collecting plates. To keep the system working efficiently, collected dust must be removed from these plates; this is commonly done using rappers, which are mechanical devices that produce strong vibrations, causing the dust to loosen and fall off, so that it can be gathered and disposed of. Hence, the correct answer to the student's question is option (a) Rappers.