The changes which take place when fats and oils are oxidised:

$A$ silver article generally turns black when kept in the open for a few days. The article when rubbed with toothpaste again starts shining.
$(a)$ Why do silver articles turn black when kept in the open for a few days? Name the phenomenon involved.
$(b)$ Name the black substance formed and give its chemical formula.

Explain the term 'Corrosion' with one example.

Explain the term 'Rancidity' with one example.

Oil and fat containing food items are flushed with nitrogen. Why?

The substances which get oxidised easily can be kept for longer duration by: