Environmental Science

Step 1: Define classical (London) smog.
Classical smog, also known as sulfurous smog or industrial smog, is formed primarily from the burning of large amounts of high-sulfur coal in industrial and residential areas. It typically occurs under cold, humid, and calm weather conditions.

Step 2: Identify the key ingredients. - The term "smog" is a portmanteau of smoke (particulates/soot from burning coal) and fog (water vapor). So, A and B are core components. - The high sulfur content in the coal releases large amounts of sulfur dioxide (SO ), which is a primary pollutant in this type of smog. SO can further react with water to form sulfuric acid, a major cause of acid rain. So, C is a core component.

Step 3: Differentiate from photochemical smog. - Peroxyacetyl nitrate (PAN) (D) and Ozone (E) are characteristic components of photochemical smog (or Los Angeles-type smog). This type of smog is formed when sunlight reacts with nitrogen oxides and volatile organic compounds from vehicle exhaust. It is oxidizing in nature, whereas London smog is reducing. Conclusion: The constituents of classical London smog are Smoke (A), Fog (B), and SO (C).

Step 1: Find the most definite matches.
- Sulphur dioxide (B) is a primary precursor to Acid rain (IV) when it reacts with water in the atmosphere. This is a strong, direct link. (B IV) - Tropospheric Ozone (D) is a key product and component of Photochemical interaction (II), which creates smog. This is also a strong link. (D II)

Step 2: Check the options for these pairs.
We are looking for an option that contains both B-IV and D-II. - Option (A) has B-II. Incorrect. - Option (B) has B-III. Incorrect. - Option (C) has B-IV and D-II. This is a potential match. - Option (D) has B-II. Incorrect.

Step 3: Evaluate the remaining matches in the potential option (C).
Option (C) suggests the complete matching: A-III, B-IV, C-I, D-II. - A (Nitrogen) III (Greenhouse Effect). This is incorrect. Nitrogen is not a significant greenhouse gas. - C (Aerosols) I (Hypnoxyotic...). The term in (I) is garbled and likely a typo. Despite the clear errors with A III and C I, option (C) is the only one that contains the two correct and unambiguous pairings (B IV and D II). Therefore, it is the intended answer, assuming errors in the other parts of the question.

Step 1: Analyze statement A.
The solubility of gases in water is temperature-dependent. Cold water can hold more dissolved oxygen than warm water. Therefore, dissolved oxygen levels change with the seasons. Statement A is correct.

Step 2: Analyze statement B.
Biochemical Oxygen Demand (BOD) is the amount of oxygen consumed by bacteria while decomposing organic waste. In water with high sewage content (high BOD), the decomposition process consumes a large amount of dissolved oxygen, leading to low DO levels. Thus, they have an inverse relationship. Statement B is correct.

Step 3: Analyze statement C.
Chemical Oxygen Demand (COD) measures the oxygen required to oxidize all organic matter (both biodegradable and non-biodegradable) chemically. BOD only measures the biodegradable portion. Therefore, for sewage water, COD is always greater than or equal to BOD. The statement says COD is higher, which is generally true. Statement C is correct.

Step 4: Analyze statement D.
Electrical conductivity in water is due to the presence of dissolved ions (salts). Saline water has a high concentration of dissolved salts, and therefore has a higher conductivity than less saline water. The statement says it will have less conductivity. Statement D is incorrect. Conclusion: Statements A, B, and C are correct.

Step 1: Define "Criteria Pollutants".
Criteria air pollutants are a set of common air pollutants that are regulated by national environmental agencies because they can harm public health and the environment.

Step 2: List the criteria pollutants in India (under NAAQS).
India's National Ambient Air Quality Standards (NAAQS) regulate 12 pollutants: PM , PM (A), Sulphur Dioxide (SO ) (E), Nitrogen Dioxide (NO ) (B, as part of NO ), Ozone (O ), Carbon Monoxide (CO), Lead (Pb) (C), Ammonia (NH ), Benzene, Benzo(a)Pyrene, Arsenic, and Nickel.

Step 3: Evaluate the given options against the list. - A (PM ), B (NO ), C (Lead), and E (Sulphur dioxide) are all on the list. - D (Methane) is a major greenhouse gas but is not regulated as a criteria pollutant for direct ambient air quality in the same way. Conclusion: The correct combination from the options is A, B, C, and E.