The correct answer is D. Marsh gas.
Methane is a colourless, odourless, non-toxic but flammable gas. It is the simplest alkane and the main component of natural gas. It is also produced by the decomposition of organic matter in swamps, landfills, and sewage treatment plants.
Blue vitriol is a blue crystalline compound of copper sulfate and water. It is also known as copper sulfate pentahydrate or bluestone. It is a common industrial chemical and is used in a variety of applications, including as a fungicide, wood preservative, and in the manufacture of other chemicals.
Laughing gas is a common name for nitrous oxide. It is a colourless, odourless gas that is used as an anesthetic and analgesic. It is also used as a recreational drug.
Heating gas is a general term for any gas that is used for heating purposes. It can include natural gas, propane, butane, and other gases.