Which of the following gases is produced from landfills?

Concept

When biodegradable organic waste decomposes without oxygen, anaerobic microorganisms convert part of its carbon into biogas. Landfill gas therefore consists mainly of methane and carbon dioxide, with only small amounts of other gases.

Application

Buried organic waste creates oxygen-poor conditions, so methanogenic microorganisms generate methane. Among the individually named gases, this directly matches methane.

Contrast

• Sulphur dioxide is chiefly associated with burning sulfur-containing fuels and with metal-smelting emissions.

• Liquefied petroleum gas is a processed fuel mixture, mainly propane and butane; it is not formed as the characteristic gas of landfill decomposition.

• More than one of the above would require at least two individually named gases to satisfy the production condition, which the offered set does not provide.

• None of the above would require every individually named gas to fail the condition, which is inconsistent with methane generation.

Cross-check

The U.S. Environmental Protection Agency describes landfill gas as a natural product of organic-waste decomposition and reports that it is roughly half methane.

Therefore, the gas produced from landfills among the offered choices is methane.