Final answer:
An uninsulated, single-shell vessel that carries liquefied gases is classified as an MC 331 tank.
Step-by-step explanation:
An uninsulated, single-shell vessel that carries gases that have been liquefied is classified as an MC 331 tank. These tanks are specifically designed to transport liquefied gases, such as liquefied petroleum gas (LPG) or liquefied natural gas (LNG), without the need for insulation. They are equipped with a single wall and are commonly used for transporting gases that have been liquefied.