Which of the following is a plant hormone?

The correct option is Cytokinin. Insulin is secreted by Islets of Langerhans of the pancreas and serves to lower the blood glucose level by stimulating the uptake of glucose by cells, specifically muscle cells, liver cells and adipose tissues cells. Thyroxine is a thyroid hormone which targets all tissues and stimulates metabolic rate, growth and development. Oestrogen is the female sex hormone secreted by developing follicles in the ovary. It serves to stimulate the growth of the uterus and the vagina, is necessary for egg maturation as well as for the development of the secondary sex characteristics in females. Thus, options Insulin, Oestrogen and Thyroxin are incorrect as these hormones are animal hormones. Cytokinins are the plant growth hormones that regulate the cell division in root and shoot of the plant both in-vivo and in-vitro. So, the correct answer is 'Cytokinin'.