Final answer:
The most relevant symptom for Rafael's doctor to assess his claim of toxic exposure to chromic acid is changes to his skin, as skin reactions are indicative of contact sensitivity to chemical irritants like chromic acid.
Step-by-step explanation:
Rafael has worked in a metal processing facility for six months and believes he has suffered toxic exposure to chromic acid. To assess his claim, the most relevant symptom his doctor would look for would be b. changes to his skin. Exposure to chemicals can lead to dermatitis, which is characterized by red, swollen, and itchy skin. Dermatitis is an example of contact sensitivity and delayed-type hypersensitivity. Symptoms like irritated eyes and difficulty breathing are also common with allergies and exposure to irritants, but given that chromium compounds are known skin irritants, skin changes would be a significant indicator of exposure to chromic acid in an industrial setting.