Final answer:
The human embryo/fetus is most sensitive to radiation during the embryonic stage of development. Exposure to radiation during this period can cause severe damage or even death of the embryo or fetus.
Step-by-step explanation:
The human embryo/fetus is most sensitive to radiation during the embryonic stage of development, which lasts from the time of implantation until the end of the eighth week after fertilization.
Radiation can harm rapidly dividing cells, which are more prominent during this stage of development. These cells include the ones forming the stomach lining, hair follicles, bone marrow, and the developing organs.
Exposure to radiation during this period can cause severe damage or even death of the embryo or fetus, and can result in impaired growth, impaired neural development, low birth weight, spontaneous abortion, and stillbirth.