Nitrogen is an inert gas that does not react with food. It prevents oxidation (rancidity) of fats and oils, thereby keeping the food fresh for longer.
The examiner expects students to state two points: (1) nitrogen is chemically inert/non-reactive, and (2) it prevents oxidation or rancidity of fats. This is a common application-based question from the Carbon and its Compounds chapter. Although the source passages do not directly state this, the concept links to unsaturated fats being prone to oxidation — nitrogen displaces oxygen, preventing this reaction.