Final answer:
A buffer solution contains a conjugate acid-base pair in reasonable concentrations and resists changes in pH when strong acids or bases are added. The most effective buffers have equal amounts of a weak acid and its conjugate base.
Step-by-step explanation:
The correct answer to the question is a buffer solution. A buffer solution contains a conjugate acid-base pair with both the acid and the base in reasonable concentrations. This kind of solution is particularly important because it resists changes in pH when small amounts of a strong acid or strong base are added. For instance, a mixture of acetic acid (CH3COOH) and sodium acetate (CH3COONa), which are a weak acid and its salt, respectively, will form an effective buffer.
It's important to note that the most effective buffer solutions contain approximately equal concentrations of the acid and its conjugate base. This composition allows the buffer to effectively neutralize additional acid or base, thereby maintaining a relatively constant pH level within the solution.