Which of the following are classified as compressed, liquefied gases?

The classification of compressed, liquefied gases is based on their physical state under pressure. Compressed gases are those that exist in the gaseous state at normal pressure but become liquid when compressed or stored under high pressure.

Ammonia, liquefied petroleum gas (LPG), and chlorine are indeed classified as compressed, liquefied gases because, when stored, they are kept at pressures high enough for them to exist in a liquid state. This property makes it convenient for storage and transport, as their volume is significantly decreased in the liquid state.

Oxygen and nitrogen typically exist as gases at normal atmospheric conditions. While they can be stored in liquid forms under extreme pressures, they are not primarily classified as liquefied gases in common usage scenarios.

Carbon dioxide, although it can exist in both solid and gas forms and is often stored in a liquefied state, is not as commonly categorized with the same industrial implications as ammonia, LPG, and chlorine.

Helium and methane, while they can also be compressed, do not have the same characteristics as the trio listed in the correct answer when interpreting industrial applications and safety data regarding their use and storage.

Thus, the correct choice encompasses the gases that fit the criteria of being compressed