In an electrostatic precipitator,

Options

A. The velocity of air between the plates must be very high to purify the air.
B. The electrode wires maintained at several thousand volts produces a corona which releases positively charged particles.
C. Particulate matter that are very small can be removed by precipitation
D. Collecting plates are grounded and collect negatively charged dust particles

Answer

**Step-by-Step Solution:**

1. **Understanding the Function of an Electrostatic Precipitator:**
An electrostatic precipitator is a device used to remove particulate matter from a gas stream, particularly in industrial applications. It works by charging the particles and then collecting them on plates.

2. **Role of Electrodes:**
The precipitator has electrode wires that are maintained at several thousand volts. This high voltage creates a corona discharge, which ionizes the air and releases electrons.

3. **Charging of Dust Particles:**
The released electrons attach to the dust particles in the air, giving them a net negative charge. This is a crucial step as it allows the dust particles to be attracted to the collecting plates.

4. **Collection of Charged Particles:**
The collecting plates are grounded, meaning they are at zero voltage. The negatively charged dust particles are attracted to these grounded plates due to the electrostatic force, allowing for the collection of particulate matter.

5. **Air Velocity Considerations:**
The velocity of air between the plates is important. It must be low enough to allow the dust particles to settle and be collected effectively. A high velocity would prevent the dust from falling onto the plates.

6. **Conclusion:**
The correct statement regarding the functioning of an electrostatic precipitator is that the collecting plates are grounded and collect negatively charged dust particles.

**Final Answer:**
The correct option is that the collecting plates are grounded and they collect negatively charged dust particles.

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