To solve this problem, we need to identify the hormone with its correct source and function. Let's analyze each option:$\newline \bullet$Option 1: Oxytocin - Posterior pituitary, growth and maintenance of mammary glands.$\newline$ - Oxytocin is indeed produced by the posterior pituitary gland.$\newline$ - However, its primary functions are to stimulate uterine contractions during childbirth and milk ejection during breastfeeding, not the growth and maintenance of mammary glands.$\newline$ - Therefore, this option is incorrect.$\newline \bullet$Option 2: Melatonin - Pineal gland, regulates the normal rhythm of sleep-wake cycle.$\newline$ - Melatonin is produced by the pineal gland.$\newline$ - It plays a crucial role in regulating the circadian rhythm, including the sleep-wake cycle.$\newline$ - Therefore, this option is correct.$\newline \bullet$Option 3: Progesterone - Corpus luteum, stimulation of growth and activities of female secondary sex organs.$\newline$ - Progesterone is produced by the corpus luteum.$\newline$ - Its primary function is to prepare the uterus for pregnancy and maintain it, not specifically to stimulate the growth and activities of female secondary sex organs.$\newline$ - Therefore, this option is incorrect.$\newline \bullet$Option 4: Atrial natriuretic factor - Ventricular wall, increases the blood pressure.$\newline$ - Atrial natriuretic factor (ANF) is actually produced by the atrial walls of the heart, not the ventricular wall.$\newline$ - Its function is to reduce blood pressure by promoting vasodilation and increasing the excretion of sodium and water by the kidneys.$\newline$ - Therefore, this option is incorrect.$\newline$Based on the analysis, the correct option is Option 2: Melatonin - Pineal gland, regulates the normal rhythm of sleep-wake cycle.