Collective nouns refer to a group of individuals or things as a single unit. Examples include:
* Team (group of people)
* Crowd (group of people)
* Flock (group of birds)
"Exhibit" is a noun that refers to an object or display that is shown to the public, often in a museum or gallery. It is not a group noun.
However, you might use the collective noun "exhibition" to refer to a collection of exhibits.