**Core Concept**
The average reproductive lifespan of an ovum refers to the duration for which an egg remains viable for fertilization. This concept is crucial in understanding female reproductive physiology, particularly in the context of fertility and assisted reproductive technologies.

**Why the Correct Answer is Right**
The correct answer is based on the fact that ova have a limited window of viability, typically around 12-24 hours after ovulation, during which they can be fertilized. After this period, the likelihood of successful fertilization and subsequent development significantly decreases.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it overestimates the lifespan.
**Option B:** This option underestimates the average reproductive lifespan of an ovum.
**Option D:** This option is also incorrect as it does not accurately reflect the known reproductive lifespan of an ovum.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that the reproductive lifespan of an ovum is short, emphasizing the importance of timely fertilization for successful conception. Understanding this concept is vital for managing infertility and planning pregnancy.

**Correct Answer:** Correct Answer: C. 24 hours.