Among all the chromosomes, what is different about a sex chromosome?

The 22 pair of chromosomes except for the pair of sex chromosomes are known as autosomal chromosomes or autosomes.

They are passed on to the progeny and determine various characters such as height, eye colour, complexion, bone structure etc where as the sex chromosomes help to determine the sex of the baby. In humans, the XX chromosome codes for a baby girl where as the XY chromosome codes for a baby boy. All other chromosomes are identical in a human but sex chromosomes are different from one another.