This question is about burning fuels in central heating boilers. In the future, gas central heating boilers may burn hydrogen rather than natural gas. Table 2 shows information about these fuels when 1 dm³ of the fuel is burned in a central heating boiler.

Explain how oxides of nitrogen are produced when burning fuels.

Oxides of nitrogen, often abbreviated as NOx (e.g., NO, NO₂), are atmospheric pollutants. They are not typically formed from the fuel itself, but from the air used in the combustion process. Air is approximately 78% nitrogen (N₂) and 21% oxygen (O₂). Normally, nitrogen is a very unreactive gas due to the strong triple bond in the N₂ molecule. However, the very high temperatures and pressures inside a combustion engine or a central heating boiler provide enough energy to break these strong bonds. This allows nitrogen and oxygen from the air to react with each other, forming various oxides of nitrogen.