Among the given options, the correct answer for a plant hormone is option 3, Gibberellin.
Option 1, Insulin, is a hormone produced by the pancreas in animals and is responsible for regulating blood sugar levels. It is not a plant hormone.
Option 2, Thyroxin, is a hormone produced by the thyroid gland in animals and is involved in regulating metabolism. It is not a plant hormone.
Option 4, Estrogen, is a hormone primarily produced by the ovaries in female animals and is responsible for the development of secondary sexual characteristics. It is not a plant hormone.
Gibberellin, on the other hand, is a plant hormone that regulates various aspects of plant growth and development. It is involved in promoting stem elongation, enhancing seed germination, breaking seed dormancy, and stimulating flowering and fruit development. Gibberellin is naturally produced in plants and affects their growth and development in a variety of ways.