Explosive, colorless, odorless gas lighter than air.

• A. Hydrogen Sulfide
• B. Carbon Dioxide
• C. BOD Test
• D. Methane Gas

Answer: (D)

The statement describes a gas that is explosive in air, colorless, odorless, and lighter than air, which fits methane best. Methane is the simplest hydrocarbon (CH4) and forms flammable mixtures with air in roughly 5% to 15% methane by volume, so it can ignite easily if there’s a source of ignition. Pure methane has no color or odor, which is why natural gas is odorized with distinct scent additives to help detect leaks. Its lighter-than-air nature means it tends to rise and accumulate near ceilings in enclosed spaces, influencing how leaks are sensed and vented. For comparison, hydrogen sulfide is also colorless and flammable but heavier than air and has a rotten-egg odor at low concentrations, while carbon dioxide is heavier than air and not explosive. The BOD test is a measurement used in water quality, not a gas. Hence, methane gas matches all the described properties.