Final answer:
The lifespan of an unfertilized egg is 24 hours, after which it deteriorates if not fertilized. This is critical for the processes of fertilization and pre-embryonic development.
Step-by-step explanation:
The lifespan of an unfertilized egg is approximately 24 hours. After ovulation, the oocyte must be fertilized within this time frame, or it will deteriorate. If fertilization occurs, the egg, which is then called a zygote, continues to develop, eventually traveling to the uterus for implantation.
This crucial development must happen within seven days post-fertilization. The process is part of the intricate sequence of pre-embryonic development, which encompasses ovulation, fertilization, cellular division, and implantation. Understanding the ovum's limited lifespan is important in the context of reproductive biology and fertility treatments. In summary, the correct answer is d) 24 hours.