Step 1: Understand female sex hormones.
The main female sex hormones are estrogens and progesterone. Among estrogens, estradiol is the most important and biologically active hormone responsible for female reproductive functions.
Step 2: Role of estradiol.
Estradiol is responsible for the development of secondary sexual characteristics such as breast development, widening of hips, and regulation of menstrual cycle. It also controls the growth and maintenance of reproductive tissues.
Step 3: Analyze the options.
(A) Glucagon: It regulates blood glucose levels, not related to reproductive system.
(B) Testosterone: It is a male sex hormone.
(C) Progesterone: It helps in maintaining pregnancy but is not primarily responsible for secondary sexual characteristics.
(D) Estradiol: Correct. It regulates menstrual cycle and development of secondary female characteristics.
Step 4: Conclusion.
Therefore, the hormone responsible is estradiol.
Final Answer:Estradiol.