Colchicine arrests cell division at

The correct option is metaphase.

Explanation:
Colchicine is an alkaloid chemical compound derived from the autumn crocus (Colchicum autumnale). It is widely known as a mitotic inhibitor or mitotic poison because of its ability to arrest cell division.

During the normal process of mitosis, spindle fibers are formed by the polymerization of tubulin proteins into microtubules. These spindle fibers attach to the kinetochores of chromosomes, aligning them along the cell's equator (metaphase plate) during metaphase, and subsequently pulling the sister chromatids apart to opposite poles during anaphase.

Colchicine works by binding to tubulin dimers, which prevents their assembly into microtubules. As a result, the formation of the mitotic spindle is inhibited. Without functional spindle fibers, the chromosomes remain scattered and cannot be pulled apart. This prevents the cell from progressing into anaphase, thereby arresting cell division at metaphase.

Because the chromosomes are highly condensed and clearly visible during this arrest, colchicine treatment is commonly used in laboratories to study chromosome structures (karyotyping) and to induce polyploidy in plant breeding.