Which OSI layer is not directly responsible for data formatting?

The Physical layer, which is the first layer of the OSI model, is primarily responsible for the transmission of raw bitstreams over a physical medium. This includes tasks such as defining electrical, mechanical, and procedural interfaces for the physical connection, as well as handling data encoding and signaling. However, the Physical layer does not concern itself with the formatting of the data itself; it simply transmits the bits that represent the data.

Data formatting—such as ensuring that data is structured in a way that can be understood across different systems—is typically the responsibility of layers higher than the Physical layer. For example, the Data Link layer (Layer 2) prepares data for transmission by encapsulating packets into frames and may also include error detection and correction. The Transport layer (Layer 4) ensures the complete data transfer between host systems through segmentation and reassembly, while the Network layer (Layer 3) is concerned with routing packets across networks.

Thus, the correct option indicates that the Physical layer is not directly involved in data formatting processes, making it the relevant choice in this context.