A 70-year-old male undergoes an elective open cholecystectomy. On post-operative day 2, he develops a fever of 101.5°F (38.6°C), tachypnea, and decreased breath sounds at the right lung base. His chest X-ray shows basilar atelectasis. What is the most likely diagnosis?

✓ Correct Answer: Option C

Post-operative atelectasis is a very common complication, especially after abdominal surgery, often presenting within 24-48 hours with fever, tachypnea, and decreased breath sounds due to shallow breathing and retained secretions. Chest X-ray findings confirm basilar atelectasis.