When studying the movement of heat, what does the term "system" refer to? what does "surroundings" refer to?

When studying the movement of heat, what does the term "system" refer to any quantity of matter of fixed identity of the chosen study. “Surroundings" refer to the rest of the universe beyond the boundary of your chosen study or system.

i'm pretty sure it is letter c.) car

it forms an anion that has a larger radius. anions have a negative charge and are larger than the original atom.