Q1: The gas which may cause explosion in sewers, is

ANS:B - methane

The gas that may cause explosions in sewers is methane. Methane is a highly flammable gas that can be produced during the decomposition of organic matter in sewage. In anaerobic conditions such as those found in sewage systems, organic materials break down and release methane gas as a byproduct of microbial activity. Methane is lighter than air and tends to accumulate in confined spaces such as sewers, where it can form explosive concentrations if not properly ventilated. Methane explosions in sewers can pose serious risks to public safety and infrastructure, making methane detection and mitigation measures important aspects of sewer maintenance and safety protocols. Therefore, methane is the gas that may cause explosions in sewers.