Introduction:
Data communication refers to the transmission of digital or analog data from one device to another through a communication link. In the case of a serial communication link, data is sent one bit at a time over a single communication channel. There are three types of data communication modes: simplex, half-duplex, and full-duplex.

Simplex:
- In simplex mode, data can only be transmitted in one direction.
- It is a unidirectional communication mode where data flows from the sender to the receiver, but not vice versa.
- Examples of simplex communication include television broadcasting and radio transmission.

Half Duplex:
- In half-duplex mode, data can be transmitted in both directions, but not simultaneously.
- It is a bidirectional communication mode where data can flow in either direction, but not at the same time.
- In this mode, a device can either send or receive data, but not both simultaneously.
- Examples of half-duplex communication include walkie-talkies and CB radios.

Full Duplex:
- In full-duplex mode, data can be transmitted in both directions simultaneously.
- It is a bidirectional communication mode where data can flow in both directions at the same time.
- In this mode, a device can send and receive data simultaneously.
- Examples of full-duplex communication include telephone conversations and internet browsing.

Conclusion:
The correct answer is option C, which states that full-duplex communication is used to send data over a serial communication link. Full duplex allows for simultaneous transmission and reception of data, which is essential in many communication scenarios. It provides a more efficient and reliable way of transmitting data compared to simplex or half-duplex modes.