What substances are typically carried in the MC 331 high pressure cargo tank?

The MC 331 high pressure cargo tank is designed specifically for the transport of liquefied gases under high pressure. This type of tank is equipped to carry substances that are gaseous at ambient temperature but can be condensed into a liquid state under pressure.

Propane and butane are the types of substances typically associated with MC 331. These gases are used widely as fuels and are stored as liquids under pressure in this type of tank. The design of the MC 331 allows it to maintain the necessary pressure to keep these substances in liquid form, making it efficient for transport and use.

Other options mentioned in the question do not align with the freight capabilities of the MC 331. Hydrogen and oxygen are typically transported in different types of containers suited for gases, while sulfuric acid and phosphoric acid, being highly corrosive, usually require specialized tankers designed to handle corrosive materials. Flammable liquids and mild corrosives could be carried in other types of cargo tanks designed for those specific classes of materials but are not the defining substances for the MC 331. Therefore, the correct answer highlights the specific use of the MC 331 for transporting propane and butane.