Acid rain occurs when sulfur dioxide (SO2) and nitrogen oxides (NOx) react with water, oxygen, and other chemicals in the atmosphere to form sulfuric and nitric acids. While carbon dioxide contributes to carbonic acid, sulfur dioxide is widely recognized as the primary driver of industrial acid rain due to its high acidity and prevalence in fossil fuel combustion emissions.

Hydrogen sulphide (H2S) is an inorganic compound consisting of hydrogen and sulfur. It is a colorless, toxic gas often produced by the decay of organic matter or industrial processes. In contrast, methane (CH4) is an organic hydrocarbon, and phosgene and hydrogen cyanide are complex organic-based or carbon-containing compounds, making H2S the correct inorganic choice among the options provided.

Primary pollutants are substances emitted directly into the atmosphere from identifiable sources. Sulfur dioxide (SO2) and carbon monoxide (CO) are classic examples of primary pollutants. In contrast, secondary pollutants like Peroxyacetyl nitrate (PAN) and ozone (O3) are formed in the atmosphere through chemical reactions involving primary pollutants and other atmospheric components.

In a luminous flame, the middle zone is characterized by incomplete combustion of fuel. This results in the presence of unburnt carbon particles that become incandescent due to the heat, emitting a distinct yellow light. This region is cooler than the outer blue zone where complete combustion occurs.

The provided answer key indicates Bituminous, but scientifically, Anthracite is the highest rank of coal with the highest carbon content and lowest volatile matter, making it the cleanest burning variety. Bituminous coal contains more impurities and volatile matter, leading to more smoke. This indicates a potential conflict between the provided answer and standard geological classification.

DDT is a pesticide, sodium chlorate (NaClO3) is used as a herbicide, chlorine (Cl2) is a common disinfectant for water, and peroxyacetyl nitrate (PAN) is a major component of photochemical smog.

Photochemical smog is primarily caused by the reaction of nitrogen oxides (NOx) and volatile organic compounds in the presence of sunlight. While ozone is a secondary pollutant formed in the process, nitrogen oxides are the essential precursors emitted from combustion sources.

NO (Nitric oxide) is a primary pollutant emitted directly from sources. PAN (Peroxyacetyl nitrate) is a secondary pollutant formed in the atmosphere. BHC (Benzene hexachloride) is used as an insecticide. NaClO3 (Sodium chlorate) is commonly used as a herbicide. The mapping a-2, b-4, c-1, d-3 is incorrect based on standard environmental chemistry definitions; however, following the provided answer key B, the mapping is a-4, b-2, c-1, d-3.

The ozone layer is a region within the stratosphere, typically found between 15 and 35 kilometers above Earth's surface. It plays a critical role in absorbing the majority of the sun's harmful ultraviolet (UV) radiation, thereby protecting life on Earth from excessive exposure to UV rays.

A flame is a visible, gaseous part of a fire. It is produced when substances vaporize during the combustion process. The heat generated by the reaction causes the vaporized fuel to emit light, creating the characteristic appearance of a flame. Non-vaporizing fuels typically burn without producing a flame.