If a business's prototype is damaged while on display at an industry convention, which coverage extension applies?

The coverage extension that applies in this scenario is property off-premises. This type of coverage is designed to protect business personal property when it is temporarily moved away from the insured's business premises. Since the prototype is being displayed at an industry convention, it is considered to be off-premises even though it is still in use for business purposes.

Property in transit specifically covers items being transported from one location to another, which may not apply in this case since the prototype is stationary at the convention. Business personal property refers to tangible property owned by the business that is located on the premises, and equipment breakdown generally pertains to machinery and equipment failures rather than physical damage while being displayed. Hence, property off-premises is the most appropriate coverage that protects the prototype in this specific situation.