Explanation:

Stop and wait ARQ (Automatic Repeat Request) is a protocol used in data communication to ensure reliable delivery of data packets between a sender and a receiver. In this protocol, the sender sends a data packet to the receiver and waits for an acknowledgment (ACK) from the receiver before sending the next packet.

To understand why the correct answer is option 'C' (n-1 acknowledgments are needed), let's break down the process step by step:

1. The sender sends the first data packet to the receiver.
2. The sender starts a timer and waits for an acknowledgment from the receiver.
3. The receiver receives the data packet and sends an acknowledgment (ACK) back to the sender.
4. The sender receives the ACK and stops the timer.
5. If the sender does not receive an ACK within a certain time (timeout), it assumes that the packet was lost or corrupted and retransmits the same packet.
6. Upon receiving the retransmitted packet, the receiver sends an ACK back to the sender.
7. The sender receives the ACK and stops the timer.
8. The sender can now send the next data packet.

Number of acknowledgments needed:
- In the stop and wait ARQ protocol, the sender can only send the next data packet after receiving an acknowledgment for the previous packet.
- So, for n data packets sent, the sender will need n-1 acknowledgments.
- The first data packet does not require an acknowledgment, as there is no previous packet to wait for.

Thus, the correct answer is option 'C' (n-1 acknowledgments are needed) because the sender needs an acknowledgment for each data packet sent, except for the first packet.

C