Which word you use for the collective noun chain?

The most common collective noun for a chain is "link."

For example: "A chain of *links* connected the two buildings."

While less common, you could also use "series" if you're talking about a chain of events, ideas, or things: "There was a series of *links* in the chain of command."

It's important to note that "chain" itself can also be used as a collective noun, especially when talking about a chain of stores, restaurants, or other businesses: "The *chain* of coffee shops was expanding rapidly."