Which layer of the OSI model is responsible for data transmission without addressing?

The Physical Layer of the OSI model is responsible for the actual transmission of raw bitstreams over a physical medium. This layer deals with the hardware aspects of sending and receiving data, including the electrical signals, light signals, and radio waves used to transmit data over different types of media. It defines the physical characteristics of the devices involved in the transmission and ensures that data is transmitted correctly without addressing.

In contrast, the other layers have specific functions that involve addressing and data organization. The Application Layer manages high-level operations like user interface and application services, while the Transport Layer is responsible for end-to-end communication and ensures error recovery and flow control, which requires addressing. The Network Layer, on the other hand, handles routing and forwarding of packets based on addressing schemes to ensure that data can be sent from source to destination through multiple networks.

Thus, the focus of the Physical Layer on the mechanical and electrical aspects of data transmission without any concern for addressing makes it the correct choice for this question.