The damage to ozone layer is caused by

Step 1: Analyze the question The question asks which substance is responsible for damaging (depleting) the ozone layer, the protective layer in the stratosphere that absorbs harmful ultraviolet (UV) radiation from the sun.

Step 2: Explain the concept Ozone (O₃) is formed and broken down naturally in the stratosphere. Certain man-made gases upset this balance and destroy ozone faster than it can be replaced. The main culprits are chlorofluorocarbons (CFCs), which were used in:

• Refrigerators and air conditioners (coolants)
• Aerosol sprays
• Foam production

Step 3: Walk through the solution

1. CFCs rise into the stratosphere.
2. UV radiation breaks them apart, releasing chlorine atoms.
3. Each chlorine atom reacts with ozone: Cl + O₃ → ClO + O₂
4. The ClO then reacts further and releases the chlorine again, so one chlorine atom can destroy thousands of ozone molecules.

Step 4: Check the options

• A. Oxygen: Wrong. Oxygen (O₂) is actually used to form ozone, so it does not damage it.
• B. Nitrogen oxide: Nitrogen oxides can contribute to some ozone breakdown in the stratosphere, but they are not the principal cause and are mainly linked to acid rain and smog.
• C. Chlorofluorocarbons: Correct. This is the classic cause of ozone depletion.
• D. Sulphur dioxide: Wrong. It mainly causes acid rain and respiratory problems.

Consequences of ozone depletion (useful for theory questions): more UV reaching Earth, leading to skin cancer, cataracts, reduced crop yield, and harm to aquatic life.

Exam tip: Remember "CFC = Chlorine Frees Carnage" for ozone. Whenever you see ozone depletion in JAMB, WASSCE or NECO, think CFCs first. Think sulphur dioxide for acid rain, and carbon dioxide/methane for global warming.