Question

Which of the following statements is correct about $\text{O}_2$ and $\text{O}_3$ molecule?

• A. $\text{O}_2$ and $\text{O}_3$ are paramagnetic
• B. The enthalpy change during the formation of $\text{O}_3$ from $\text{O}_2$ is positive
• C. The entropy change in the formation of $\text{O}_3$ from $\text{O}_2$ is positive
• D. $\text{O}_3$ is more stable than $\text{O}_2$

Hint:

Ozone formation requires energy (like UV light), so it is endothermic (+$\Delta H$).

Answer 1

The Correct Option is B

Step 1: Concept Ozone ($\text{O}_3$) is an allotrope of oxygen ($\text{O}_2$) formed by an endothermic process.

Step 2: Meaning $3\text{O}_{2(g)} \rightarrow 2\text{O}_{3(g)}$; $\Delta H = +284.5 \text{ kJ/mol}$.

Step 3: Analysis $\text{O}_2$ is paramagnetic, but $\text{O}_3$ is diamagnetic. Entropy decreases because 3 moles of gas become 2 moles. Ozone is thermodynamically unstable and decomposes back to oxygen.

Step 4: Conclusion The formation of ozone is endothermic, so the enthalpy change is positive. Final Answer: (B)