I THINK THAT A monotremes is the answer.
first
placenta
The Placenta uses a the process of diffusion to diffuse the nutrients from the mothers blood into the babies. Then the umbilical cord carries the nutrients to the baby to the Placenta. Answer is Placenta
True
this is the function of the placenta, the mothers blood flows through capillaries that run very close to capillaries filled with the fetus' blood and the gases diffuse across due to the higher oxygen affinity of fetal haemoglobin.
how nutrients,oxygen and waste are exchange between the fetus and the mother
For Plato the answer is provide the fetus with oxygen and nutrients and eliminate carbon dioxide and other wastes from the fetus All the above
Mammals, such as kittens, have a cord that connects them to the placenta. The placenta transfers food and oxygen to the baby while it is growing. That cord, the umbilical cord, goes from the placenta to the navel (or, on a cat, where the navel would be). Sometimes that cord can get wrapped around part of the body during birth.
If your question was 'What is the oxygen compound that absorbs UV radiation?' - then ozone
A mammalian embryo gets oxygen and nutrients from it mother by means of the umbilical cord which extends the embryonic blood supply into the placenta embedded in the mothers womb. The blood supply in the placenta is close to that of the mother and oxygen and nutrients diffuse across from the mother to the baby. With egg laying animals the nutrients are supply to the embryo as the yolk part of the egg and oxygen is supplied by diffusion through the permeable shell and shell membrane
All mammals obtain their oxygen from the air.
The young of placental mammals develop within a placenta. The placenta is a thick membrane that is connected to the inside of the uterine wall. The umbilical cord connects the baby to the inside wall of the placenta. Nutrients and oxygen go from the mother's blood stream through the placenta, down the umbilical cord, and into the baby. The baby releases waste products and carbon dioxide, which travel up the umbilical cord, through the placenta and into the mother's blood stream.