Explanation:

The correct option is (D) Inversion. An inversion is a chromosomal rearrangement where a segment of a chromosome breaks off, flips 180 degrees, and reattaches, resulting in the reversal of the gene order within that segment. For example, a segment $\text{A-B-C}$ becomes $\text{A-C-B}$. Option (A) Deletion involves the loss of a chromosomal segment. Option (B) Duplication is the repetition of a chromosomal segment. Option (C) Translocation is the movement of a chromosomal segment to a different, non-homologous chromosome. None of these describe a reversal of gene order within a segment.