Answer:
1) When there is only one car dealership in a small town, giving the dealership the ability to influence the price of cars, market failure is due to MARKET POWER.
2) When a manufacturing plant dumps chemical waste into a nearby river, poisoning the water supply for a small town downstream, market failure is due to EXTERNALITY.
Explanation:
The car dealership has an excessive market power , which refers to the firms ability to increase the price of its products (cars) above the price of a competitive market.
When the manufacturing plant dumps chemical wastes into the river, it is causing a negative externality on the town's water supply. This means that the town (which is a third party in this case) is suffering from the actions of another party's economic transactions.