The fraction of bilirubin that is water-soluble and reacts with Diazo reagent without adding an accelerator is:
B) Conjugated
Conjugated bilirubin, also known as direct bilirubin, is water-soluble and can be detected with Diazo reagent without the need for additional accelerators. Unconjugated bilirubin requires an accelerator to react with Diazo reagent. Total bilirubin is a combination of both conjugated and unconjugated bilirubin, and indirect bilirubin is synonymous with unconjugated bilirubin.