Final answer:
Rh incompatibility occurs when the mother is Rh-negative and the baby is Rh-positive. This can result in the mother's immune system producing antibodies against the Rh factor.
Step-by-step explanation:
In Rh incompatibility, the mother and baby have different Rh factors. The mother's immune system can produce antibodies against the Rh factor if she is Rh-negative and exposed to Rh-positive fetal blood cells. This can happen during the last trimester of pregnancy or during delivery. Therefore, the most likely scenario for Rh incompatibility is when the mother is Rh-negative and the baby is Rh-positive (b) Mother Rh-negative, baby Rh-positive.