**Core Concept**
Estrogen metabolism in postmenopausal women involves a complex interplay of enzymes and hormonal pathways. After menopause, the ovaries cease to produce significant amounts of estrogen, leading to a shift in estrogen metabolism.

**Why the Correct Answer is Right**
Estrogen is primarily metabolized by the enzyme 17β-hydroxysteroid dehydrogenase (17β-HSD), which converts estradiol to estrone. This conversion is more pronounced in postmenopausal women due to the decreased activity of the enzyme aromatase, which is responsible for converting androgens to estrogens. As a result, estrone becomes the predominant form of estrogen in postmenopausal women.

**Why Each Wrong Option is Incorrect**
**Option A:** Estriol is a weak estrogen that is primarily produced during pregnancy. Its levels are significantly reduced in postmenopausal women.

**Option C:** Estradiol is the most potent form of estrogen and is predominantly produced by the ovaries in premenopausal women.

**Option D:** Androstenedione is a weak androgen that is a precursor to estrogen production, but it is not a product of estrogen metabolism.

**Clinical Pearl / High-Yield Fact**
In postmenopausal women, the increased levels of estrone are associated with a higher risk of osteoporosis and cardiovascular disease, making estrone a key player in the pathophysiology of these conditions.

**✓ Correct Answer: B. Estrone**