Think about the chemical equation.
If oxygen is being added then which kind of reaction it would be?
See which element/compound is getting oxidized
Which element(s)/compound(s) are being reduced/oxidised here ?
Think about the things that characterized oxidation/reduction
Which element(s)/compound(s) are being reduced/oxidised here ?
This gas has the highest percentage in the composition of air.
What is the common name for oxidation of foods