Q.Discuss briefly the following:

1. Greenhouse gases Greenhouse gases are atmospheric gases that absorb infrared (heat) radiation reflected from the Earth's surface and re-radiate it back, trapping heat in the atmosphere in a natural process called the greenhouse effect. The major greenhouse gases are carbon dioxide (from fossil-fuel combustion and deforestation), methane (from paddy fields, cattle and landfills), nitrous oxide (from fertiliser use and combustion), chlorofluorocarbons (from refrigerants and aerosols), and water vapour. While the natural greenhouse effect keeps Earth warm enough to sustain life, human activities have sharply increased the concentration of these gases, intensifying the effect and causing global warming.
2. Catalytic converter A catalytic converter is a pollution-control device fitted into the exhaust system of automobiles. It contains catalysts — typically the expensive metals platinum, palladium and rhodium — which speed up chemical reactions that convert harmful exhaust gases into less harmful ones: unburnt hydrocarbons and carbon monoxide are oxidised to carbon dioxide and water, while nitrogen oxides are reduced to nitrogen and oxygen. Because leaded petrol coats and deactivates these catalysts, vehicles fitted with a catalytic converter must run on unleaded (lead-free) petrol.
3. Ultraviolet B …

Write each of the three as a short, self-contained note covering what it is, its mechanism, and its significance: greenhouse gases (identity + heat-trapping mechanism + link to warming), catalytic converter (location, catalysts, the specific conversions it performs, the unleaded …

• Listing only carbon dioxide as a greenhouse gas and omitting methane, nitrous oxide, CFCs and water vapour.
• Describing the catalytic converter's function without naming the specific conversions (CO/hydrocarbons → CO2/water; nitrogen oxides → nitrogen/oxygen) or the unleaded-petrol requirement. …