Why ARQ stands for Automatic Repeat reQuest: the receiving station checks each packet's error-detecting code and reports back. A positive acknowledgment (ACK) tells the sender the packet arrived intact and it may move on, while a negative acknowledgment (NAK) says the check failed, so the sender must send that packet again. This handshake is what lets modes like AMTOR, PACTOR and packet radio deliver error-free data over noisy HF paths.
Watch out The choice saying the packet was received without error describes an ACK, the opposite response; NAK is the error report, not the all-clear.
N in NAK = No good, send it again. ACK = All Correct, Keep going.