If copper is kept open in air,it slowly loses its shining brown surface and gains a green coating. It is due to the formation of

$A$ 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.

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

Write true or false for the following statement:
Due to corrosion, iron gets a brown coating, copper gets a green coating, and silver gets a black coating.

The marble statues are often slowly corroded when kept in the open for a long time. Give a suitable reason.

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