A dwarf plant can be stimulated to grow to normal height by the application of...

Explanation

Some plants are naturally small or dwarf, but it is possible to stimulate them to grow to normal height. The question asks which substance can be applied to a dwarf plant to make it grow to normal height. The options are thyroxin, gibberelin, insulin, and kinin. Thyroxin is a hormone produced by the thyroid gland in animals, and has no effect on plants. Insulin is a hormone produced by the pancreas in animals, and also has no effect on plants. Kinin is a plant hormone that is involved in stress responses and growth regulation, but it does not stimulate growth to normal height in dwarf plants. The correct answer is gibberelin. Gibberelin is a plant hormone that promotes stem elongation and cell division, and can stimulate dwarf plants to grow to normal height. It is used in agriculture to increase the height of crops such as rice and wheat, and in horticulture to promote growth in ornamental plants. In summary, the substance that can be applied to a dwarf plant to make it grow to normal height is gibberelin, which is a plant hormone that promotes stem elongation and cell division.