Which is not a vestigial organ in man?

Nails

Among the options listed, nails are not considered a vestigial organ in humans.

Vestigial organs are structures that have reduced in size or lost their original function during the course of evolution. They are remnants of organs or structures that were functional in the ancestral species but have diminished or no apparent function in the current species.

In humans:

• The nictitating membrane (or the third eyelid) is vestigial; it's a small, undeveloped fold of tissue in the inner corner of the eye.
• Tail vertebrae are vestigial remnants of a tail present during early human embryonic development.
• The vermiform appendix is considered vestigial.
• On the other hand, nails are not regarded as vestigial organs.