Which of the following is not a vestigial organ in human beings?

Vestigial organs are those organs, tissues, or cells in the body of an organism that are no longer functioning the way they use to in their ancestral form. 

The gall bladder is a small pear-shaped organ located under the liver in the digestive system of humans. It receives bile juice from the liver and stores it for some time before releasing it into the small intestine.

Appendix, sinuses, coccyx, wisdom tooth, external ears, nictitating membranes, and tonsils are the vestigial structures that still persist in the human body.

Thus, the gall bladder is a functional organ and not vestigial in human beings.