Final answer:
Goodwill is the long-term asset that cannot be separated and sold as it is tied to the company's reputation and relationships.
Step-by-step explanation:
The only long-term asset that cannot be separated from the business and sold is goodwill. Goodwill is an intangible asset that arises when a buyer acquires an existing business. It represents the value of the business's reputation, customer relationships, employee relations, and other factors that are not physically tangible or separable from the business entity itself. In contrast to tangible assets like collectibles, real estate, or equipment, which can be sold separately, goodwill is tied to the company as a whole and cannot be sold independently.