Final answer:
Fetal heart tones are the most important assessment for a client in the 8th week of pregnancy experiencing spotting and a rigid abdomen, as they give direct insight into the fetus' condition.
Step-by-step explanation:
The most important assessment for a client in the 8th week of pregnancy who is spotting, has a rigid abdomen, and is on bed rest is fetal heart tones. This is because fetal heart tones are a direct indication of the vitality and current status of the fetus. Spotting and a rigid abdomen could be signs of an imminent miscarriage or an ectopic pregnancy, both of which necessitate immediate attention to the fetal condition. On the other hand, protein in the urine might indicate pre-eclampsia, which is less likely this early in pregnancy; cervical dilation assessment is important but may not provide direct information about the fetus' well-being at this moment; hematocrit level, while important for understanding the mother's blood status, is less critical than fetal heart tones for immediate fetal assessment.