___________________ is the operating pressure of an oxygen regulator.

The correct choice indicates that the operating pressure of an oxygen regulator typically falls within the range of 0 to 100 psig (pounds per square inch gauge). This is accurate because oxygen regulators are designed to safely control and deliver pure oxygen gas to various applications, such as in welding, cutting, or medical use. The specified pressure range ensures that the gas is delivered at a manageable level, which is crucial for both safety and effective operation of the equipment.

Operating above this range could introduce risks such as leaks or uncontrolled gas flow, while operating below may not provide adequate performance for the intended application.

In contrast, the other ranges would be inappropriate for standard oxygen regulators due to either being too low, which could undermine the necessary flow and pressure for effective application, or too high, which could lead to safety hazards and breaches of regulatory standards.