Which item is at the Physical Layer of the OSI model?

The correct answer is B. Switch port. The Physical Layer of the OSI model is concerned with the physical transmission of signals across network media, including electrical or optical signaling, cabling, connectors, transceivers, and physical interfaces. HPE Aruba Networking hardware and transceiver documentation describes switch ports, transceiver slots, copper cabling, fiber-optic cabling, and link LEDs as physical connection components. A switch port is therefore the only option listed that belongs directly to the Physical Layer. Option A, URL, is associated with application-level access to web resources and is not a Physical Layer item. Option C, IP address, belongs to Layer 3 because it is used for logical addressing and routing. Option D, TCP port, belongs to Layer 4 because TCP ports identify transport-layer application sessions. Although a switch port may participate in Layer 2 switching after a link is established, the physical connector/interface itself is part of the Layer 1 network infrastructure. This makes “switch port” the correct answer from the listed options.