What is one disadvantage of using gas flames for heating flammable liquids?

Using gas flames for heating flammable liquids presents a significant fire and explosion hazard, which is why this option is the correct choice. When a gas flame is employed near flammable liquids, any vapors produced can ignite, leading to dangerous situations such as flashback, where flames can travel back to the source of flammable vapors, or even full combustion if the right conditions are met. This risk is exacerbated in laboratory settings where flammable liquids are often present, making it critical to implement proper safety precautions and alternative heating methods that do not involve open flames.

While it is true that inefficiency, the need for special equipment, and time consumption could be concerns in some contexts, they do not capture the immediate and potentially catastrophic risks posed by using open flames around flammable substances. The potential for a fire or explosion is a fundamental safety concern that outweighs these other factors.