Final answer:
Water should never be used to put out a grease fire because it can cause splattering and spread the fire. Baking soda, a Class B or K fire extinguisher, or salt should be used instead.
Step-by-step explanation:
The item that should NEVER be used to put out a grease fire is water. When water is applied to a grease fire, it can cause the oil to splatter and spread the fire further, making the situation much more dangerous. The correct extinguishing agents for a grease fire include baking soda, a fire extinguisher designed for grease fires (often a Class B or K extinguisher), or salt. These substances work by smothering the fire and cutting off the oxygen supply required for combustion.