Final answer:
A switch sends out LLDP advertisements every 30 seconds by default, which is used to communicate its identity and capabilities to other devices(option b).
Step-by-step explanation:
In the context of network communications, the Link Layer Discovery Protocol (LLDP) is used by devices like switches to advertise their identity, capabilities, and neighbors to other devices on the same network segment. A switch will typically send out LLDP advertisements b) every 30 seconds by default.
However, it's worth noting that the frequency of LLDP advertisements can sometimes be adjusted through the switch's configuration settings, allowing network administrators to tailor LLDP advertisement intervals to their specific network requirements.