Which gas generated during anaerobic decomposition is known for its flammability?

Methane (CH4) is the gas generated during anaerobic decomposition that is recognized for its flammability. During anaerobic conditions, microorganisms break down organic matter, resulting in the production of methane as a byproduct. This gas is highly combustible and can pose significant safety hazards in environments where it accumulates, such as landfills or poorly ventilated areas where organic waste is decomposing.

In the context of the other options, carbon dioxide is a non-flammable gas produced during various biological processes, but it does not support combustion. Nitrous oxide, while a greenhouse gas and a contributor to environmental issues, is not flammable itself. Oxygen, on the other hand, is a supporter of combustion but is not produced during anaerobic decomposition. Therefore, the characteristics of methane make it the correct answer due to its significant role as a flammable gas generated in anaerobic environments.