When you fill a glass with cold water from a faucet and then let the glass sit undisturbed for two hours you will see small bubbles sticking to the glass. What are the bubbles?

The small bubbles that form on the glass when cold water sits undisturbed are primarily composed of dissolved gases, mainly oxygen and nitrogen, which are released from the water as it warms slightly to match the temperature of the surrounding air. This process is called degassing, where the solubility of gases decreases with temperature. As the water sits, these gases come out of solution, forming visible bubbles that cling to the glass surface.