Pick out the incorrect statement.

Options

A. `I_(2)O_(5)` is formed by heating `HIO_(3)` to `170^(@)C`
B. `I_(2)O_(5)` is stable to heat
C. `I_(2)O_(5)` is used in the estimation of CO
D. `I_(2)` combines with `O_(3)` to form `I_(4)O_(9)`. When heated above `75^(@)C`, it `(I_(4)O_(9))` decomposes to form `I_(2)O_(5)`.

Answer

To solve the question of identifying the incorrect statement regarding iodine oxides, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement 1: I2O5 is formed by heating HIO3 to 170 degrees Celsius.**
- When HIO3 (iodic acid) is heated to about 170 degrees Celsius, it decomposes to form I2O5 (iodine pentoxide) and water (H2O) as a byproduct. The balanced chemical equation for this reaction is:
\[ 2 \text{HIO}_3 \rightarrow \text{I}_2\text{O}_5 + \text{H}_2\text{O} \]
- This statement is **true**.

2. **Statement 2: I2O5 is stable to heat.**
- I2O5 is not stable when heated. Upon heating above 350 degrees Celsius, it decomposes into iodine vapor (I2) and oxygen gas (O2). The balanced equation for this decomposition is:
\[ 2 \text{I}_2\text{O}_5 \rightarrow 4 \text{I}_2 + 5 \text{O}_2 \]
- Therefore, this statement is **incorrect**.

3. **Statement 3: I2O5 is used in the estimation of CO.**
- I2O5 can react with carbon monoxide (CO) to produce iodine (I2) and carbon dioxide (CO2). The balanced reaction is:
\[ 5 \text{CO} + \text{I}_2\text{O}_5 \rightarrow \text{I}_2 + 5 \text{CO}_2 \]
- This statement is **true**.

4. **Statement 4: Iodine combines with ozone to form I4O9, which decomposes to form I2O5 when heated above 75 degrees Celsius.**
- The reaction of iodine with ozone produces I4O9, and upon heating, I4O9 decomposes to form I2O5 and iodine. The balanced equation is:
\[ 2 \text{I} + 3 \text{O}_3 \rightarrow \text{I}_4\text{O}_9 \]
\[ \text{I}_4\text{O}_9 \rightarrow 2 \text{I}_2\text{O}_5 + 2 \text{I} \]
- This statement is **true**.

### Conclusion:
The only incorrect statement is **Statement 2: I2O5 is stable to heat**.

---