A high-pressure intermodal tank is commonly used to transport __________.

A high-pressure intermodal tank is designed specifically for the transportation of liquefied gases. These tanks are built to handle the substantial pressures associated with keeping gases in a liquid state, making them suitable for transporting materials such as propane, butane, and other industrial gases. The design ensures that the integrity of the tank maintains safety during transport, addressing both pressure and potential volatility of the contents.

In contrast, solid waste is typically transported in containers designed to manage solid materials, while chemical spills refer to incidents rather than the contents of a transportable unit. Acids and bases can be transported in specially designed containers, but they do not generally require the high-pressure specs that liquefied gases do. Therefore, the focus on pressure and the physical state of the material being transported confirm that liquefied gas is the correct answer.