What is the term for an auto that the insured acquires because the auto described in the declarations page has been damaged to the point of being permanently unusable?

The correct term for an auto that the insured acquires when their previously insured vehicle has been damaged beyond repair is a "replacement auto." This designation is essential in auto insurance policies since it outlines how the coverage applies to newly acquired vehicles when the original vehicle is no longer usable.

In the context of an insurance policy, a replacement auto is specifically meant to replace a vehicle that has been classified as a total loss. This means that the damage to the original vehicle is so severe that it is considered permanently unusable for its intended purpose. When the insured purchases or acquires a new vehicle due to this situation, it is critical that the policy provides coverage for it under the "replacement auto" provision.

The other options describe different types of vehicles which do not specifically address this scenario. A new auto typically refers to a vehicle that has just been purchased, usually within a certain timeframe, while a substitute auto generally refers to a vehicle that is temporarily used to replace a vehicle that is not operational for reasons other than it being permanently unusable. An additional auto refers to any extra vehicles acquired by the insured that may not necessarily be in direct replacement of another. Hence, "replacement auto" is the most accurate term in this context.