Which of the following is a source of methane?

The correct answer is (a) Wetlands.

Wetlands are a type of ecosystem that is saturated with water, either permanently or seasonally. They are home to a variety of plants and animals, and they play an important role in the environment. Wetlands are a source of methane, a greenhouse gas that is more potent than carbon dioxide. Methane is released from wetlands when organic matter decomposes in the absence of oxygen.

The other options are incorrect.

(b) The foam industry is not a source of methane.

(c) Thermal power plants are a source of carbon dioxide, not methane.

(d) The cement industry is a source of carbon dioxide, not methane.