Question

Which electromagnetic wave is most likely to keep your food warm.

Answer 1

Frequency between infra-red and ultraviolet includes radiowaves, microwaves and visible light.
So radios and cellular phones use radiowaves, while we see with the aid of visible light.
Heating food safely might be done with microwaves. Depending on how hot the object is, they will emit different proportions of the different frequencies of light. If you heat a metal, at first you won't see anything because the radiation is in the infrared range, but as you continue to heat, it becomes red hot then yellow and eventually blue. Some stars are so hot that they give off ultraviolet.