Here's what happens:

* Reaction: When tin is exposed to air, it reacts with oxygen to form tin oxide (SnO2).

* Appearance: This oxide forms a dull, grayish-white layer on the surface of the tin, known as tarnish.

* Protection: The oxide layer actually protects the tin from further corrosion.

Other gases that can react with tin:

* Chlorine: Tin reacts with chlorine gas to form tin chloride (SnCl2 or SnCl4).

* Hydrogen sulfide: Tin reacts with hydrogen sulfide to form tin sulfide (SnS or SnS2). This reaction is responsible for the "tarnished" look of some tin objects over time.

However, tin is generally considered to be quite resistant to corrosion compared to other metals, due to the protective oxide layer.