Answer:
a chemical reaction
Step-by-step explanation:
What has happened to the statue of liberty is that a chemical reaction has occurred to the materials making up this edifice.
The statue is made up of copper. On reacting with oxygen, it undergoes an oxidation.
This makes the copper to rust and decolorize.
It implies that copper has reacted with oxygen in air and possibly from water.
This gives a new product.
We know this because for most chemical changes, they give new products and are not easily reversible.