The $pH$ of blood is maintained by carbon dioxide and ${H_2}C{O_3}$ in the body and chemical constituents of blood. This phenomenon is called.
A) Colloidal.
B) Buffer action.
C) Acidity.
D) Salt balance.

Hint:We know Bohr Effect related to the hemoglobin and it is inversely related to acidity. Bohr Effect refers to the shift in the dissociation curve caused by the concentration of carbon dioxide which helps in increasing the efficiency of oxygen transportation through blood.

Complete step by step answer:

The bicarbonate buffer system is an acid-base homeostatic mechanism involving the balance of acid \[\left( {{{\text{H}}_2}C{O_3}} \right)\], bicarbonate ion \[\left( {HC{O_3}^ - {\text{ }}} \right)\], and carbon dioxide so as to take care of pH within the blood, and among other tissues, to support proper metabolic function.
Human blood contains a buffer of acid \[\left( {{{\text{H}}_2}C{O_3}} \right)\], and bicarbonate anion \[\left( {HC{O_3}^ - {\text{ }}} \right)\] so as to take care of blood pH between\[7.35\], and \[7.45\] as a value above \[7.8\] or less than \[6.8\] can cause death. During this buffer, hydronium and bicarbonate anion are in equilibrium with acid.
The reaction is,
\[C{O_2} + {H_2}O \rightleftharpoons {H_2}C{O_3} \rightleftharpoons {H^ + } + HC{O_3}^ - \]

Therefore, the option B is correct.

Note:
We also know about the details of carbon monoxide poisoning:
Carbon dioxide can readily associate and dissociate from hemoglobin, other molecules like carbon monoxide gas cannot. Carbon monoxide gas features a greater affinity for hemoglobin than oxygen. Therefore, when carbon monoxide gas is present, it binds to hemoglobin preferentially over oxygen. As a result, oxygen cannot bind to hemoglobin, and there is no oxygen transported through the body .Carbon monoxide may be a colorless, odorless gas and is therefore difficult to detect. Carbon monoxide gas can cause headaches, confusion, and nausea; long-term exposure can cause brain damage or death. Administering pure oxygen is the usual treatment for carbon monoxide gas poisoning.