$(a)$ Differentiate between biodegradable and non-biodegradable substances.
$(b)$ How is acid rain causing harm to the 'Taj Mahal'?
$(c)$ What is smog?

(N/A) Biodegradable substances are those that can be broken down into simpler,harmless substances by biological processes (decomposers). They do not cause long-term pollution. Example: Organic waste.
Non-biodegradable substances are those that cannot be broken down by biological processes. They persist in the environment and cause significant pollution. Example: Plastic.
$(b)$ Acid rain contains high concentrations of sulfuric and nitric acids. When it falls on the 'Taj Mahal',it reacts with the calcium carbonate $(CaCO_3)$ present in the marble,leading to its corrosion and the formation of pits,which causes the monument to lose its luster and structural integrity.
$(c)$ Smog is a type of air pollution that is a mixture of smoke and fog. It often forms in industrial areas or cities with high vehicular traffic.