When food containing fat or oil is not used and left for a long time, their smell and state changes. Name the process which is responsible for this change . List two methods to prevent or slow down the above change.

Explanation

When food contaning fat or oil is not used and left over for a long time, their smell and state changes because fats and oils are getting slowly oxidised . This process is called rancidity.
Two methods which are used to slow down the oxidiation process are :
(i) keeping food in airtight container
(ii) Flushing the bags containing food with nitrogen gas.