Pick out the incorrect statement.

Options

A. Except nitrogen , all the elements of group 15 exist in allotropic modification
B. Only at high temperature , greater than 1,070 K, phosphorus dissociates into `P_2` molecules
C. Red phosphorus is obtained by heating white phosphorus at 540 - 570 K in the absence of air for several hours
D. White phosphorus is more reactive , but less soluble in `CS_2` (and other organic solvents ) than red phosphorus

Answer

To solve the question, we need to analyze each statement provided and determine which one is incorrect. Here’s a step-by-step breakdown:

### Step 1: Analyze the First Statement
**Statement:** "Except nitrogen, all the elements of group 15 exist in allotropic modification."

- **Explanation:** Group 15 elements include nitrogen, phosphorus, arsenic, antimony, and bismuth. Nitrogen does not have allotropes, while phosphorus has several allotropes (red, white, and black). Therefore, this statement is **true**.

### Step 2: Analyze the Second Statement
**Statement:** "Only at high temperatures greater than 1070 Kelvin, Phosphorus dissociates into P2 molecules."

- **Explanation:** Phosphorus does indeed dissociate into P2 molecules at high temperatures, specifically above 1070 Kelvin. Thus, this statement is **true**.

### Step 3: Analyze the Third Statement
**Statement:** "Red phosphorus is obtained by heating white phosphorus at 540-570 Kelvin in the absence of air for several hours."

- **Explanation:** This statement is accurate. Red phosphorus is produced by heating white phosphorus under the specified conditions. Therefore, this statement is **true**.

### Step 4: Analyze the Fourth Statement
**Statement:** "White phosphorus is more reactive but less soluble in CH2 and other organic solvents than red phosphorus."

- **Explanation:** This statement is **false**. White phosphorus is indeed more reactive than red phosphorus, but it is actually more soluble in organic solvents like carbon disulfide (CS2), while red phosphorus is insoluble in these solvents.

### Conclusion
After analyzing all four statements, we find that the fourth statement is incorrect.

### Final Answer
The incorrect statement is: **"White phosphorus is more reactive but less soluble in CH2 and other organic solvents than red phosphorus."**