Upon which principle does the complete combustion of gas rely?

The principle that complete combustion of gas relies on is the availability of excess oxygen. Complete combustion occurs when there is sufficient oxygen to allow a fuel (in this case, gas) to react fully, producing carbon dioxide and water as the primary products. This process is optimal when there is an adequate supply of oxygen to ensure that all of the fuel can react, thus preventing the formation of carbon monoxide, which is a byproduct of incomplete combustion.

When there is excess oxygen present, it ensures that the fuel can combust efficiently, maximizing energy release and minimizing harmful emissions. In contrast, if oxygen is limited, incomplete combustion occurs, leading to the production of less desirable byproducts such as carbon monoxide, which can be dangerous and indicates inefficient fuel usage.

The other choices do not directly relate to the principle of complete combustion. The presence of carbon is a component of the fuel but does not influence combustion completeness. High pressure conditions can affect combustion dynamics but are not a necessary condition for complete combustion. Similarly, low temperature conditions typically hinder combustion efficiency, as higher temperatures are generally conducive to better combustion processes. Thus, the focus on excess oxygen as a crucial factor in achieving complete combustion stands out as the correct answer.