The correct option is Physical layer because it does not belong to the TCP/IP protocol stack.

The TCP/IP model is typically described with four layers called Link, Internet layer, Transport layer, and Application layer. Those four are the layers used in TCP/IP and the name Physical does not appear as a separate TCP/IP layer.

Physical layer is part of the OSI seven layer model and it deals with electrical signals and physical media. Those physical functions are usually considered part of the TCP/IP Link or network interface layer rather than a separate layer in TCP/IP.

Internet layer is incorrect because the Internet layer is a core TCP/IP layer that handles logical addressing and routing with protocols such as IP.

Transport layer is incorrect because the Transport layer is part of TCP/IP and it provides end to end communication services with protocols like TCP and UDP.

Application layer is incorrect because the Application layer is part of TCP/IP and it encompasses high level protocols such as HTTP, SMTP, and DNS that provide services to user applications.

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