Determine the correct statement from the given option with respect to an electrostatic precipitator .

Options

A. the velocity of air is very fast so that a large volume of air can be purified at a time .
B. the electrode wires maintained at several thousand volts produces a corona which releases positively charged particles.
C. air is passed through a spray of water and lime .
D. Collecting plates are grounded and collect negative charged dust particles .

Answer

To determine the correct statement regarding an electrostatic precipitator, let's analyze each option step by step.

### Step 1: Understand the Function of an Electrostatic Precipitator
An electrostatic precipitator is a device used to remove particles from a gas (usually air) by using electrostatic forces. It works by charging dust particles and then collecting them on plates that have an opposite charge.

### Step 2: Analyze Each Option
1. **Option A**: "The velocity of air is very fast, so that the large volume of air can be purified at a time."
- **Analysis**: This statement is incorrect. If the velocity of air is too fast, the electrostatic precipitator cannot effectively charge and collect the particles. A slower airflow allows more time for the particles to interact with the charged surfaces.

2. **Option B**: "The electrode wire maintained at several thousand volts produces a corona which releases positively charged particles."
- **Analysis**: This statement is also incorrect. The electrode wire does produce a corona discharge, but it releases negatively charged particles (electrons), not positively charged ones.

3. **Option C**: "Air is passed through a spray of water and lime."
- **Analysis**: This statement is incorrect as well. While water and lime may be used in some air purification processes, they are not part of the functioning of an electrostatic precipitator.

4. **Option D**: "Collecting plates are grounded and collect negatively charged dust particles."
- **Analysis**: This statement is correct. The collecting plates are indeed grounded and attract the negatively charged dust particles, allowing them to be collected effectively.

### Conclusion
After analyzing all the options, the correct statement regarding an electrostatic precipitator is:
**Option D: Collecting plates are grounded and collect negatively charged dust particles.**