Name a common high-pressure refrigerant used in industrial systems.

Ammonia (NH3) is commonly used as a high-pressure refrigerant in industrial refrigeration systems due to its efficiency and effectiveness in heat transfer. It is particularly favored in large-scale applications such as food processing and cold storage because it has a high cooling capacity and a low environmental impact when managed properly. Additionally, ammonia has a high pressure at operational temperatures, making it suitable for industrial applications that require robust cooling solutions and system reliability.

The other options, while they may be refrigerants, are not typically characterized as high-pressure refrigerants in the same way as ammonia. Freon was historically a generic term for various chlorofluorocarbons but has largely been phased out due to environmental concerns. R-404A is a blend used in commercial refrigeration, but it operates at lower pressures compared to ammonia. R-134A is used in a variety of applications, but it is primarily suited for low-pressure systems rather than high-pressure industrial environments.