All permitted antifreeze chemicals are __________.

The correct choice notes that all permitted antifreeze chemicals are heavier than water. This is important because the density of a fluid affects how it behaves in a fire protection system. Antifreeze solutions must remain in the pipes and not allow for the design pressure to be exceeded, as lighter fluids can easily move or float to the top of a system, potentially leading to uneven flow distribution.

In addition to density considerations, antifreeze must operate effectively throughout a range of temperatures, especially in systems exposed to freezing conditions. By being heavier than water, these antifreeze solutions can maintain their position in the pipe network, ensuring that they can provide adequate protection against freezing while also fulfilling the system's hydraulic requirements. This property helps to ensure that pressure remains consistent and effective during operation. Therefore, understanding the density of antifreeze chemicals is crucial when selecting and applying these solutions in sprinkler systems.