Which one of the following chemicals induces polyploidy in plant cells?

The correct option is D Colchicine
Colchicine is an alkaloid prepared from the dried corns and seeds of Colchicum autumnale, the autumn crocus or meadow saffron. It is often used to induce polyploidy in plants. Basically, the colchicine prevents the microtubule formation during cell division, thus the chromosomes do not pull apart like they normally do. This results in double the number of chromosomes that it would normally have. If this cell divides again, then the doubled number of chromosomes are passed to the offspring cells. Plants that have more than the normal two sets of chromosomes are termed as polyploids.

Thus, the correct answer is option D.