**Core Concept**
The FDA guidelines for medical termination of pregnancy involve a sequential administration of two drugs: Mifepristone, a progesterone receptor antagonist, and Misoprostol, a prostaglandin E1 analog. This regimen aims to induce uterine contractions and ultimately expel the fetus.

**Why the Correct Answer is Right**
Mifepristone is administered first to block the action of progesterone, essential for maintaining pregnancy. After 24-48 hours, Misoprostol is given to stimulate uterine contractions by releasing prostaglandins, which induce labor and facilitate the expulsion of the fetus. This sequential administration ensures effective termination of pregnancy while minimizing side effects.

**Why Each Wrong Option is Incorrect**
**Option A:** 6 hours - This timing is too early for Misoprostol administration, as it does not allow sufficient time for Mifepristone to take effect and induce uterine contractions.
**Option B:** 72 hours - This timing is excessively long and may increase the risk of complications, such as infection or retained products of conception.
**Option C:** 12 hours - This timing is too short, as Mifepristone requires a longer duration to effectively block progesterone receptors and induce uterine contractions.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the FDA guidelines for medical termination of pregnancy emphasize the importance of a 24-48 hour interval between Mifepristone and Misoprostol administration to ensure efficacy and minimize complications.

**Correct Answer: B. 48 hours**