When a Bunsen burner is lit and not being used for heating things, a _________ flame should be used. What one word completes this sentence?

The word that completes the sentence is "safety."

When a Bunsen burner is lit but not being used for heating purposes, it is crucial to use a safety flame. This type of flame is more controlled and less visible, making it less hazardous in a laboratory setting. It is generally a yellow, luminous flame that is cooler and is used primarily to avoid accidents, especially when the burner is not actively being utilized for experiments. Using a safety flame adds a level of precaution, reducing the risk of burns, fires, or unintended ignition of flammable materials nearby. It's an essential practice in laboratory safety protocols.