Answer: `gcloud compute instances list.`

The correct command is `gcloud compute instances list.` This command lists Google Compute Engine instances, including both internal and external IP addresses. Other options like `gcloud compute networks list-ip.`, `gcloud compute networks list.`, and `gcloud compute instances list-ip.` are incorrect because they either do not support the action `list-ip` or do not list IP addresses as required. For more details, refer to the Google Cloud SDK documentation.

Author: LeetQuiz Editorial Team