The contents of a gas cylinder are only determined by __________.

The correct choice is determined by reading the cylinder label, as it provides essential and detailed information regarding the contents of the gas cylinder. The label typically includes the type of gas, its specific properties, safety instructions, and any hazards associated with its use. Reliable identification of the gas is crucial for safe handling and application in various contexts.

While inspecting the cylinder may provide visual cues about the condition of the cylinder itself, it does not guarantee accurate knowledge of the contents inside. Similarly, checking the pressure gauge could give an indication of the remaining gas but does not inform you about the type of gas contained. An analysis of cylinder contents can determine what is inside, but this method is more complex, often requiring specialized equipment or procedures, making it less practical than simply reading the label for immediate identification.