Final answer:
The important buffer in body fluids is NaHCO3 (sodium bicarbonate).
Step-by-step explanation:
A buffer in body fluids is NaHCO3 (sodium bicarbonate).
Buffers are substances that help maintain a stable pH in a solution by resisting changes in acidity or alkalinity. In the body, the bicarbonate system acts as an important buffer. It consists of the weak acid carbonic acid (H2CO3) and its conjugate base, bicarbonate ion (HCO3-). When there is an increase in acids, the bicarbonate ion can combine with them to form carbonic acid, preventing the pH from dropping too low. On the other hand, when there is an increase in bases, carbonic acid can dissociate to form bicarbonate ion, preventing the pH from rising too high.
Therefore, the correct answer is D) NaHCO3.