What type of gas compound is considered to be highly pressurized?

The correct choice identifies compressed gas as a type of gas compound that exists in a highly pressurized state. Compressed gases are contained in pressurized cylinders or tanks, and they can be in liquid, vapor, or a mixture of both states, depending on their temperature and pressure. The high pressure allows these gases to be stored compactly and can facilitate their use in various applications, such as welding, refrigeration, and laboratory settings.

Compressed gases can release significant energy when they are allowed to expand rapidly, which can be a safety hazard if proper precautions are not taken. Hence, knowledge of how to handle and store compressed gases safely is crucial for personnel working in environments where these substances are present.

The other types of compounds listed do not inherently imply high pressure. Flammable gases can exist at atmospheric pressure and require a specific mix with air to ignite; oxidizers enhance combustion but may not necessarily be under pressure; and water reactive substances do not signify any specific gas state related to pressure.