Which of the following statements about ozone is true?

• A. Ozone is a colorless and odorless gas under standard conditions.
• B. Ozone is commonly found in the Earth's troposphere at high concentrations.
• C. Ozone (O_3) is a molecule composed of three oxygen atoms.
• D. Ozone is less reactive than molecular oxygen (O_2).

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the molecular structure of ozone. Ozone (O_3) is indeed composed of three oxygen atoms bonded together, which distinguishes it from the more common diatomic oxygen molecule (O_2).
2. Step 2: Consider the physical properties of ozone under standard conditions (25°C and 1 atm). Ozone is actually a pale blue gas with a distinct sharp odor, so it is not colorless or odorless.
3. Step 3: Examine the typical locations and concentrations of ozone in the atmosphere. Ozone is primarily found in the stratosphere, forming the ozone layer, and is present in much lower concentrations in the troposphere, where it acts as a pollutant rather than being abundant.
4. Step 4: Compare the reactivity of ozone to molecular oxygen. Ozone is more reactive than O_2 due to its molecular structure and the presence of a weaker bond, making it a strong oxidizing agent.
5. Step 5: Based on these points, identify the true statement: Ozone (O_3) is a molecule composed of three oxygen atoms.