Final answer:
The organelle that is not surrounded by a double membrane is the Golgi apparatus.
Step-by-step explanation:
The organelle that is not surrounded by a double membrane is the Golgi apparatus.
Both the Mitochondrion and Chloroplast have a double membrane because they originated from endosymbiotic bacteria that took residence inside eukaryotic cells. The double membrane is a remnant of the bacterial cell wall.
In contrast, the Nucleus is also surrounded by a double membrane.