Maximum action of corpus luteum is at ……… day:

**Core Concept**
The corpus luteum is a temporary endocrine structure in the female ovaries that plays a crucial role in the menstrual cycle and early pregnancy. Its primary function is to produce progesterone, which prepares the uterus for implantation of a fertilized egg and maintains pregnancy.

**Why the Correct Answer is Right**
The corpus luteum reaches its maximum action around 7-8 days after ovulation, which is the time when the fertilized egg is expected to implant in the uterine lining. The luteinizing hormone (LH) surge triggers the formation of the corpus luteum, and its progesterone production peaks during this period. Progesterone helps to thicken the uterine lining, making it receptive for implantation.

**Why Each Wrong Option is Incorrect**
**Option A:** The corpus luteum starts to regress and its progesterone production decreases after 7-8 days, making this option incorrect.
**Option B:** The corpus luteum is formed after ovulation, but its maximum action is not at the time of ovulation itself. This option is incorrect.
**Option C:** While the corpus luteum is active throughout the luteal phase, its maximum action is not at the beginning of the phase. This option is incorrect.

**Clinical Pearl / High-Yield Fact**
The corpus luteum's progesterone production is essential for maintaining early pregnancy. A deficiency in progesterone can lead to early pregnancy loss.

**Correct Answer: B. 7-8 days**