The following factors would contribute to environmental pollution except

Step 1: Analyze the question We need the one factor that does NOT contribute to environmental pollution.

Step 2: Review each option

• A. Production of ammonia (Haber process): It uses natural gas or other fuels to make hydrogen, which releases CO₂. Ammonia leaks and fertilizer runoff also cause air and water pollution. Pollutes.
• B. Manufacture of cement: Heating limestone (CaCO₃ → CaO + CO₂) releases large amounts of CO₂. The process also gives off dust and other gases. Pollutes.
• C. Photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (in the presence of light and chlorophyll). Plants take in carbon dioxide and release oxygen. This is a natural process that cleans the air and helps balance atmospheric gases. Does not pollute.
• D. Combustion: Burning fuels produces CO₂, CO, soot and oxides of sulphur and nitrogen. Pollutes.

Step 3: Answer Photosynthesis is the only process that helps the environment rather than polluting it, so it is the exception.

Correct answer: C

Tip: In "except" questions, look for the option that is natural or beneficial while the others are industrial or involve burning. Remember that photosynthesis removes CO₂ and adds O₂, while combustion and industrial processes do the opposite.