Explanation:

In the OSI (Open Systems Interconnection) model, network communication is conceptually divided into seven distinct layers, each with specific responsibilities. **Analysis of Options:** * **Option (A) Transport layer:** This layer (Layer 4) is primarily responsible for end-to-end communication, segmentation of data, and flow control. While security protocols like TLS/SSL often operate over the transport layer to secure communication, the *general function* of encryption and decryption of application data, as a service provided by the OSI model, is not primarily attributed to this layer. * **Option (B) Session layer:** This layer (Layer 5) is responsible for managing communication sessions, including establishing, maintaining, and terminating connections between applications. It does not handle encryption or decryption of data content. * **Option (C) Presentation layer:** Correct. This layer (Layer 6) is responsible for data translation, compression, and encryption/decryption. Its main role is to ensure that data is presented in a format that the application layer can understand, handling syntax and semantics. This is the layer where data is typically encrypted before transmission and decrypted upon reception to maintain data confidentiality and integrity. * **Option (D) Switch:** A switch is a network hardware device that operates primarily at the Data Link Layer (Layer 2) or sometimes the Network Layer (Layer 3) of the OSI model. It is not a layer itself, and its function is to forward data frames or packets within a local area network, not to perform encryption or decryption of data content.