Which of the following statements is not true about ozone ?

Explanation

To determine which statement about ozone is not true, we will analyze each statement provided.

### Step 1: Analyze Statement A
**Statement A:** Ozone is an allotrope of oxygen.

- **Explanation:** Allotropes are different forms of the same element. Oxygen exists in two main allotropes: diatomic oxygen (O2) and ozone (O3). Therefore, this statement is true.

### Step 2: Analyze Statement B
**Statement B:** The ozone layer protects the Earth's surface from the excessive concentration of harmful ultraviolet radiation.

- **Explanation:** The ozone layer absorbs a significant portion of the Sun's harmful ultraviolet (UV) radiation, protecting living organisms on Earth. Thus, this statement is also true.

### Step 3: Analyze Statement C
**Statement C:** The conversion of oxygen into ozone is an exothermic process.

- **Explanation:** The conversion of O2 to O3 is actually an endothermic process, meaning it requires energy input. The enthalpy change (ΔH) for this reaction is positive (approximately +24.5 kJ/mol), indicating that energy is absorbed. Therefore, this statement is false.

### Step 4: Analyze Statement D
**Statement D:** Ozone is a more powerful oxidizing agent than molecular oxygen.

- **Explanation:** Ozone (O3) can release nascent oxygen, which is a very strong oxidizing agent. This makes ozone a more powerful oxidizing agent compared to diatomic oxygen (O2). Thus, this statement is true.

### Conclusion
After analyzing all statements, the statement that is not true about ozone is **Statement C**, which claims that the conversion of oxygen into ozone is an exothermic process.

### Final Answer
**C**: The conversion of oxygen into ozone is an exothermic process. (This statement is not true.)

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