Final answer:
Mashed potatoes are not suitable for a full-liquid diet because they cannot be fully liquefied to meet the diet's requirements.
Step-by-step explanation:
The full liquid diet includes all foods that are liquid or can turn to liquid at room or body temperature. Given the options, mashed potatoes are not appropriate for a patient on a full-liquid diet because they cannot be liquefied completely without significant modification. Items like ice cream, tomato soup, and coffee are suitable as they meet the criteria of being liquid or able to turn into a liquid without additions. This means that this diet is suggested when a person is not able to move their jaws.