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( Article Type: Explanation )

Nitrogen is a colourless, odourless gas that comprises 78% of the atmosphere. Nitrogen is cycled between the air and the soil in the nitrogen cycle, which includes a process known as nitrogen fixation. Nitrogen fixation can be carried out by industry (to make fertilisers) or naturally by micro-organisms producing combined nitrogen as ammonia and nitrates, which are absorbed by plants from the soil and used to make proteins for nutrition. Nitrogen Oxide (N2O) is a colourless gas with a sweet odour, which is used as a weak anaesthetic (‘laughing gas’). Nitrogen Dioxide (NO2) is a red-brown toxic gas, which is one of the products of vehicle combustion and is an active part of smog.