If a router has four interfaces and each interface is connected to four switches, how many broadcast domains are present on the router?

A single broadcast domain would be the result if a Layer 2 switch connected all devices, but routers segment traffic and create multiple domains.

Two broadcast domains would require only two active router interfaces, not four as described in the scenario.

Routers do not forward broadcast traffic between interfaces, meaning each interface defines the boundary of a distinct broadcast domain. With four interfaces, there are exactly four broadcast domains. The switches connected to each interface extend that single broadcast domain but do not create additional ones.

Eight broadcast domains would only exist if additional segmentation - such as four switches each configured with two separate VLANs - were present, which is not described.