........... is an example of full duplex system.

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Accepted Answer

The correct option is (4):
The concept of a duplex system refers to the direction of signal transmission within a communication channel. A Full Duplex System allows data or signals to be transmitted simultaneously in both directions between two connected devices. The classic and most accurate example that illustrates this capability is the **Telephone**. When two individuals are engaged in a standard telephone conversation, both can speak and hear one another at the exact same moment. The communication channel is entirely open for bidirectional and concurrent data flow, which is the defining characteristic of a full duplex system, leading to the natural, efficient, two-way interaction we experience.

The incorrect option is (1):
A **Keyboard** is an example of a **Simplex** communication system. Simplex mode dictates that data can only travel in a single, predetermined direction. For a keyboard, the signal flow is strictly from the input device (the keyboard) to the computer (the receiver). The computer cannot send complex data or signals back through the primary data path to the keyboard. Although there are minor exceptions like signaling light status (Caps Lock), the main function is unidirectional input. Therefore, it lacks the two-way, bidirectional communication necessary for any duplex system.

The incorrect option is (2):
A **Monitor** is also fundamentally a **Simplex** device. Its role is solely for output, meaning the data flow is unidirectional from the computer's graphics hardware to the display. It receives information and displays it to the user. A monitor is not designed to transmit data back to the computer, which immediately disqualifies it from being considered a duplex system. It is a passive recipient of the visual information generated by the computer, supporting only one direction of communication.

The incorrect option is (3):
A **Walkie-Talkie** operates as a **Half Duplex** system. While the communication channel in a half duplex system is bidirectional, the key constraint is that only one device can transmit at a time. Users must take turns, often signaling the end of their transmission by saying "over." If both parties attempt to speak simultaneously, their signals will interfere, and neither message will be successfully transmitted. This crucial limitation of non-simultaneous communication prevents the walkie-talkie from being classified as a full duplex system.