Which gases are released in order when coal heats up?

When coal is subjected to heat, it undergoes a process known as pyrolysis, which involves the decomposition of organic material through thermal decomposition. The various gases released during this process occur in a specific sequence based on the temperature and the chemical reactions taking place.

The correct option includes gases like carbon dioxide and carbon monoxide first, which are formed from the breakdown of carbon in the coal. As coal continues to heat, it releases volatile matter, which includes a variety of hydrocarbons. Methane emerges as one of the primary gases produced from the breakdown of the coal's organic components.

As temperatures rise further, lighter hydrocarbons such as hydrogen and ethane may also be released. Ethylene can appear later in the process as it is a product of the cracking of heavier hydrocarbons. This sequence reflects the gradual breakdown of complex organic materials in coal into simpler gas molecules.

Overall, the option that mentions carbon dioxide and carbon monoxide first accurately captures the sequence in which these gases are released as coal heats up, representing the natural progression of pyrolysis in coal.