The conversion of ferric chloride (FeCl₃) to ferrous chloride (FeCl₂) is not specifically called "degradation." Instead, it is a type of chemical reaction known as a reduction reaction. In this process, ferric chloride (FeCl₃), which contains iron in the +3 oxidation state, gains electrons and is reduced to ferrous chloride (FeCl₂), where iron is in the +2 oxidation state. The reduction reaction involves the gain of electrons, leading to a decrease in the oxidation state of iron.

Answer: A) Sulphur dioxide Explanation: Air pollutants are solid particles, gases, and liquid droplets in the air that can adversely affect ecosystems and the health of humans.   Major ambient air pollutants include toxic metals, polycyclic aromatic hydrocarbons, benzene, particulate matter (PM), nitrogen oxides, sulfur oxides, carbon monoxide, and ozone. Power plants, factories, and vehicle and air traffic are the most important anthropogenic sources of air pollution.   In addition, natural sources such as wildfires and volcanic activity contribute to ambient air pollution.