Answer: Option (c) is correct.
Step-by-step explanation:
There are two types of externality:
(a) Positive externality
(b) Negative Externality
Externality refers to a cost or benefit to a person from the actions or activities of other person.
If a set of actions decreases the utility of the third person who is not included in the activity then it is a negative externality.
If a set of actions increases the utility of the third person who is not included in the activity then it is a Positive externality.