The correct answer is option 2, Estrogen. Estrogen is a hormone that is primarily responsible for the development of female sexual characters. It is produced by the ovaries and plays a crucial role in the menstrual cycle, breast development, and the development of secondary sexual characteristics in females. These secondary sexual characteristics include the growth of breasts, widening of hips, and the development of pubic and underarm hair.

Prolactin, option 1, is another hormone that is produced by the pituitary gland and plays a role in milk production and breastfeeding, but it is not directly responsible for the development of female sexual characters.

Oxytocin, option 3, is a hormone that is involved in childbirth and breastfeeding. While it is important for reproductive processes, it does not directly lead to the development of female sexual characters.

Progesterone, option 4, is a hormone that is primarily involved in preparing the uterus for pregnancy. Although progesterone is important for reproductive processes, it is not directly responsible for the development of female sexual characters.

Therefore, option 2, Estrogen, is the correct answer.