Answer : 2. "colon"
Explanation :

In humans, the tailbone, also known as the coccyx, is a small triangular bone located at the base of the spine. It is made up of three to five fused (joined together) vertebrae and is the remnant of a tail that our evolutionary ancestors used for balance and communication. The coccyx is not attached to the colon; rather, it is a part of the vertebral column and provides support for the pelvic organs.