Final answer:
The duodenum is not an intraperitoneal organ.
Step-by-step explanation:
The intraperitoneal organs are organs that are located within the peritoneal cavity, which is a membrane-lined cavity in the abdomen. The peritoneum is a serous membrane that covers the abdominal organs and lines the abdominal wall. The organs that are intraperitoneal include the liver, spleen, and ileum. The duodenum, on the other hand, is not an intraperitoneal organ as it is retroperitoneal, meaning it lies behind the peritoneum.