Which of the following is an example of a buffer?

salt

hemoglobin

metal

plasma

The correct answer is just hemoglobin

Answer: Letter A, B, C, D (all choices are buffers)

The salt, hemoglobin, metal and plasma all act as a buffer where they all confer resistance to a change in the pH of a solution when hydrogen ions or hydroxide ions are added or removed. The salt is an ionic compound containing an anion of sodium ion (Na+), and chloride ion (Cl-) other than OH - and O2-, this is a solution of a weak acid and it's conjugate base that makes it a buffer. A metal-ion buffer solution contains the free (hydrated) metal ion along with a compound formed by the association of the ion.

In addition, the most significant buffer of blood is hemoglobin where Histidine residues accept protons and act as buffers. Moreover, plasma proteins are buffers but the absolute amount is small compared to the intracellular protein.