Q1: In sewers the gas generally found, is

ANS:E - All the above.

• Hydrogen sulphide (H2S): Hydrogen sulphide is a common gas found in sewers, especially in anaerobic conditions where organic matter decomposes. It has a characteristic foul odor similar to rotten eggs.
• Carbon dioxide (CO2): Carbon dioxide can be present in sewers due to the decomposition of organic matter and the respiration of microorganisms. It is produced as a byproduct of microbial metabolism.
• Methane (CH4): Methane may also be present in sewers, particularly in anaerobic environments where organic matter undergoes decomposition. Methane is a flammable gas and is generated by the anaerobic digestion of organic materials.
• Petrol vapours: Petrol vapors are not typically found in sewers unless there is a specific contamination event or if there are leaks from underground storage tanks or pipelines. Petrol vapors are volatile and can pose safety hazards in confined spaces.

Therefore, the correct option is: All the above. Hydrogen sulphide, carbon dioxide, and methane are commonly found gases in sewers due to the decomposition of organic matter and anaerobic conditions. However, petrol vapors are not typically associated with sewers unless there are specific contamination events.