What is a negative externality of drinking a can of caffeine-free, diet soda?

the cost of natural resources and energy to produce the can in the factory

the lack of calories in the soda

the space that the empty can will take up in a landfill if not recycled

the lack of caffeine in the soda

The correct answer is the third option, the space that the empty can will take up in a landfill if not recycled properly. If empty cans were not recycled properly, they would take up a lot of space in landfills and won't be able to decompose, since it is made out of aluminum, which would be hard to decompose, therefore the negativity of drinking a caffeine-free soda is the improper disposal of the empty can itself.