Which of the following is not correct about DPD?

Options

A. Its the decrease of diffusion pressure
B. Maximum value of DPD is equal to OP
C. DPD of pure `H_2O` is zero
D. Increase in TP of a cell decreases DPD

Answer

To determine which of the following statements about Diffusion Pressure Deficit (DPD) is incorrect, we need to understand the concept of DPD and analyze the given options.

### Step-by-Step Solution:

1. **Understanding DPD**:
- DPD stands for Diffusion Pressure Deficit. It refers to the difference between the osmotic pressure (OP) and the turgor pressure (TP) in a plant cell.
- Mathematically, DPD can be expressed as:
\[ \text{DPD} = \text{Osmotic Pressure (OP)} - \text{Turgor Pressure (TP)} \]

2. **Analyzing the Statements**:
- **Option 1**: "It is a decrease in diffusion pressure."
- This statement is correct because DPD indicates a deficit or decrease in diffusion pressure.

- **Option 2**: "Maximum value of DPD is equal to OP."
- This statement is also correct. When turgor pressure is zero, DPD equals the osmotic pressure.

- **Option 3**: "DPD of pure water is 0."
- This statement is incorrect. The DPD of pure water is not zero; it is actually a measure of the potential for water to move, which can be influenced by solutes.

- **Option 4**: "Increase in turgor pressure of cell decreases DPD."
- This statement is correct. If turgor pressure increases, the value of DPD decreases since DPD is calculated as OP - TP.

3. **Identifying the Incorrect Statement**:
- From the analysis, we find that **Option 3** ("DPD of pure water is 0") is the incorrect statement about DPD.

### Conclusion:
The statement that is not correct about DPD is **Option 3**.

---