The correct answer is a - III, b - I, c - IV, d - II. Explanation & Key Takeaways: • The below table is correctly matched. • +------------------------+------------+ | Pollutant | Medium | +------------------------+------------+ | Nitrogen oxides | Air | | Petroleum hydrocarbons | Sea | | Fluorides | Freshwater | | Mycotoxins | Food | +------------------------+------------+ Important Notes: • UNEP • The United Nations Environment Programme is responsible for coordinating the UN's environment-related activities and assisting developing countries in having environmentally sound policies and practices. • Founded: 5 June 1972. (That's why World Environment Day is celebrated on 5 June every year.) • Headquarters location: Nairobi, Kenya. • UNEP is the leading global environmental authority that sets the global environmental agenda. • Promotes the coherent implementation of the environmental dimension of sustainable development. • Serves as an authoritative advocate for the global environment. Related Concepts: • Other pollutants and their sources • Nitric oxide (NO) • Produced during the burning of fuel at higher temperatures. (e.g. road vehicles, heaters). • Sulfur dioxide (SO2) • Fossil fuel combustion (principally power stations), conversion of wood pulp to paper, manufacture of sulphuric acid, smelting, incineration. • Carbon Monoxide (CO) • Forms when carbon fuels are burned, either in the presence of too little oxygen or at a very high temperatures.