The correct option is C Colchicine
Colchicine is a chemical used in plant breeding techniques. It can be used to induce polyploidy. Thus, option C is correct.
Cytokinins are a class of plant growth substances that promote cell division, or cytokinesis, in plant roots and shoots.
IAA refers to indole acetic acid. It helps in leaf formation, development of embryo etc.
Nitrous acid acts as mutagen.