Question

Heat transfer by radiation depends on _____.
a medium that transmits heat
movement within a liquid
solid objects in contact with one another
electromagnetic waves

Answer 1

This should just be a standard definition that you can find in your book. There's nothing to really think about here, just look at the definition for "Heat transfer by radiation"

Answer 2

Radiation does not require a medium to move which eliminates the first 3 options.