Final answer:
When the pH of blood is higher than the isoelectric point of hemoglobin, hemoglobin will have a net negative charge. Since the blood pH is 7.4 and the isoelectric point of hemoglobin is 6.9, hemoglobin in the blood is negatively charged. The option (B) is correct.
Step-by-step explanation:
If the isoelectric point of hemoglobin is 6.9 and the pH of blood is 7.4, this implies that the pH of the blood is above the isoelectric point of hemoglobin. At its isoelectric point (pI), a molecule is electrically neutral because the positive and negative charges balance out.
Since the pH of the blood is higher (more alkaline) than the pI of hemoglobin, hemoglobin in the blood will have a net negative charge. Therefore, the correct answer is: b) Hemoglobin is negatively charged.