The correct answer is (d). The pH level of blood of a normal person is 7.35-7.45. This is slightly alkaline, which helps to protect the body from damage caused by acids. The pH level of blood is regulated by a number of mechanisms, including the kidneys, lungs, and blood buffers. If the pH level of blood falls outside of the normal range, it can lead to serious health problems, such as acidosis or alkalosis.
Option (a) is incorrect because the pH level of blood is not typically in the range of 8.25-8.35. Option (b) is incorrect because the pH level of blood is not typically in the range of 4.5-4.6. Option (c) is incorrect because the pH level of blood is not typically in the range of 6.45-6.55.