What happens when the fat and oil containing food materials are left outside for a long time?
- (a)Fats and oils in the food get oxidized
- (b)Fats and oils in the food get reduced
- (c)Fats and oils in the food get ice-covered
- (d)No reaction takes place
Correct — A, Fats and oils in the food get oxidized. When fat- or oil-rich food is left exposed to air for a long time, the oxygen in the air reacts with the fats and oils and oxidizes them. This oxidation is what turns the food rancid, giving it a bad smell and taste. So the change that takes place is oxidation of the fats and oils.
- (b)Fats and oils in the food get reduced — Reduction is the opposite of what happens. On exposure to air the fats gain oxygen (are oxidized), not reduced, so this is wrong.
- (c)Fats and oils in the food get ice-covered — Food left 'outside' at ordinary temperature does not become ice-covered. Freezing needs sub-zero temperatures and is unrelated to the spoiling of fatty food in open air.
- (d)No reaction takes place — A reaction clearly does take place — the fats oxidize and the food turns rancid. Saying nothing happens is false.
Fats and oils exposed to air slowly react with oxygen. This oxidation of fats and oils is called rancidity, and it produces the unpleasant smell and taste of spoiled fatty food. It is a chemical change caused by atmospheric oxygen acting on the fat molecules over time.
The trigger word is 'left outside for a long time' — that means exposure to air, and air means oxygen. Fats reacting with oxygen is oxidation (rancidity). That immediately rules out 'reduced' (the opposite), 'ice-covered' (needs freezing, not air) and 'no reaction' (something clearly does happen).
- Oxidation of fats and oils on exposure to air is called rancidity.
- It gives spoiled fatty food its characteristic bad smell and taste.
- Rancidity is slowed by antioxidants, airtight packing and flushing with nitrogen gas.
- Refrigeration also slows the oxidation by lowering the reaction rate.
- Choosing 'reduced' — the fats gain oxygen, so they are oxidized, not reduced.
- Reading 'left outside' as 'refrigerated' and picking ice-covered.
Everyday chemistry is asked as a real-life change to identify — link the spoiling of fatty food to oxidation/rancidity.
No directly related past PYQ was found.
- practice — not a real PYQ
The process by which fats and oils in food get oxidized on exposure to air, giving a bad smell and taste, is called
- (a)Fermentation
- (b)Rancidity
- (c)Hydrogenation
- (d)Saponification
Answer(b) Rancidity — the oxidation of fats and oils on exposure to air.
- practice — not a real PYQ
Which of the following helps slow down the rancidity of packaged fatty foods?
- (a)Adding water
- (b)Flushing the pack with nitrogen gas
- (c)Exposing it to sunlight
- (d)Adding extra oxygen
Answer(b) Flushing the pack with nitrogen gas — it keeps oxygen away and slows oxidation.