A bright metal turns dull over time due to oxidation. What is this process called?

The correct option is Corrosion.

Explanation:
When a bright metal is exposed to air, moisture, and other gases in the atmosphere, it reacts with oxygen to form a metal oxide layer on its surface. This process of oxidation causes the metal surface to lose its metallic luster and turn dull over time.
The gradual deterioration and eating away of metals due to chemical reactions with their environment (primarily oxygen, moisture, and acids) is known as corrosion. Rusting of iron and tarnishing of silver are common examples of this process.

Why other options are incorrect:
- Sublimation is the physical transition of a substance directly from the solid state to the gas state without passing through the liquid state.
- Filtration is a physical method used to separate insoluble solid particles from a liquid using a filter medium.
- Evaporation is the process by which a liquid changes into a gas or vapor, typically at temperatures below its boiling point.