Which is the lowest layer of the OSI model?

• A. Data Link Layer
• B. Physical Layer
• C. Network Layer
• D. Transport Layer

Answer: (B)

The lowest layer is the one that handles the actual transmission of raw bits over a physical medium. It defines the electrical/optical signaling, timing, cabling, connectors, and other hardware-focused details that enable devices to place and read bits on a wire. It doesn't interpret data or perform any end-to-end functions; it simply moves the binary signal from one device to another. Above it, the data link layer deals with framing, MAC addressing, and error detection on a single link, the network layer handles routing and logical addressing across networks, and the transport layer manages end-to-end delivery and reliability. So the bottom-most layer is the one dedicated to physical transmission of bits.