Final answer:
Gravy should be reheated in a microwave to an internal temperature of 165°F (74°C) to ensure it is safe to eat.
Step-by-step explanation:
The internal temperature to which gravy should be reheated in a microwave is 165°F (74°C). This temperature ensures that any potential bacteria are killed, making the gravy safe for consumption. According to food safety guidelines, reheating foods to this internal temperature reduces the likelihood of foodborne illnesses.