Explanation:

- Methane is indeed colorless, odorless, and flammable, commonly referred to as marsh gas. It forms naturally in wetlands due to the decay of organic matter.

- Option 1: Laughing gas is actually nitrous oxide, used as an anesthetic and not related to methane.

- Option 2: Heating gas could refer to methane, as it is used in cooking and heating, but this isn’t a common name or synonym.

- Option 3: Blue vitriol is copper(II) sulfate, unrelated to methane.

- Option 4: Marsh gas is a known term for methane due to its natural occurrence in marshes.

Marsh gas is the correct answer.