Which characteristic means that propane is considered safe in its natural state?

Propane's safety in its natural state is attributed to its characteristics as being colorless and odorless. While propane itself is not toxic, its lack of color and odor could pose a risk since a leak might not be immediately detectable without additional safety measures. To enhance safety, an odorant is added to propane, giving it a distinctive smell, which allows for the detection of leaks. This is a critical aspect of propane safety; if it were inherently detectable, it would allow individuals to take precautions before any dangerous situations arise. The other characteristics listed do not pertain to propane's natural state or safe handling in the way that being colorless and odorless does.