Understanding Data Transmission Modes
Data transmission refers to the transfer of data between devices. The mode of transmission can significantly affect the performance and efficiency of data communication systems.

Types of Transmission Modes
1. **Asynchronous Transmission**
- In this mode, data is sent without synchronization with a clock signal.
- Data packets are sent at irregular intervals, often leading to overhead due to start/stop bits.
2. **Parallel Transmission**
- Parallel transmission sends multiple bits simultaneously over multiple channels.
- This increases speed but is limited by physical constraints like cable size and signal interference.
3. **Serial Transmission**
- Serial transmission sends one bit at a time over a single channel.
- It is simpler and cost-effective but can be slower compared to parallel transmission.
4. **Isochronous Transmission**
- Isochronous transmission ensures that data is sent at consistent intervals, synchronized with a clock signal.
- It is crucial for applications requiring constant timing, such as audio and video streaming, where data must arrive at precise intervals.

Why Isochronous is the Correct Answer
- The question specifies "one bit is sent for each clock cycle," which aligns perfectly with the definition of isochronous transmission.
- This mode guarantees that data is transmitted in a regular, timed manner, making it ideal for real-time applications.

Conclusion
In summary, the correct option for the mode of transmission where one bit is sent for each clock cycle is **Isochronous (D)**, as it emphasizes synchronized timing crucial for effective data communication.