Which of the following is incorrect ?

Options

A. When `NO_2` is dissolved in cold water , a mixture of nitrous and nitric acid is formed
B. When `NO_2` is dissolved in hot water , the same reaction occurs as that in cold water
C. `N_2O_5` is made by the reaction of `P_4O_(10)` with nitric acid vapours
D. `NO_2` is very corrosive gas and reacts directly with a number of metals

Answer

To determine which statement is incorrect regarding the behavior of nitrogen dioxide (NO2) and its reactions, let's analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding the Dissolution of NO2 in Cold Water:**
- When NO2 is dissolved in cold water, it forms a mixture of nitrous acid (HNO2) and nitric acid (HNO3). This is a well-known reaction where NO2 reacts with water to produce these acids.
- **Conclusion:** This statement is correct.

2. **Understanding the Dissolution of NO2 in Hot Water:**
- In hot water, the behavior of NO2 changes. It can lead to the formation of nitrogen oxides such as NO and NO2, and primarily nitric acid (HNO3) is formed.
- **Conclusion:** This statement is also correct.

3. **Corrosiveness and Reactivity of NO2:**
- NO2 is known to be a highly corrosive gas that reacts with many metals. This is due to its paramagnetic nature and the presence of an unpaired electron, making it highly reactive.
- **Conclusion:** This statement is correct as well.

4. **Formation of N2O5:**
- The statement regarding the formation of N2O5 from the reaction of P4O10 with nitric acid vapors is also accurate. N2O5 can be formed under specific conditions involving phosphorus pentoxide and nitric acid.
- **Conclusion:** This statement is correct.

### Final Evaluation:
After analyzing all the statements, it appears that all provided statements are correct. Therefore, the question "Which of the following is incorrect?" does not have a valid answer based on the provided options.