Final answer:
The minimum pipe size for medical gas systems is not provided in the options; it is determined by relevant codes and standards like NFPA 99, based on factors like flow rates and pressure.
Step-by-step explanation:
The minimum size pipe allowed in medical gas systems is typically determined by various codes and standards, and can vary depending on the specific application and jurisdiction. However, none of the options provided (1/2 inch, 3/4 inch, 1 inch, 2 inch) explicitly state the minimum size for medical gas systems. In practice, sizes are often dictated by factors such as the required flow rates, pressure, and the type of gas being delivered. It's important to consult the relevant codes and standards, such as the National Fire Protection Association (NFPA) 99 Health Care Facilities Code or local building codes, to determine the correct minimum pipe size for a specific medical gas system.