Receiving delicious food is to escaping electric shock as is to

positive reinforcer; negative reinforcer

Explanation:

positive reinforcer; negative reinforcer

Receiving delicious food can be seen as a positive reinforcer while escaping electric shock can be seen as a negative reinforcer.

molecules are free to separate from each other and will take on the shape of the container. molecules move completely at random and high speeds. they vibrate in a fixed position and do not move around much. molecules expand to the edge of their container.