Final answer:
Option d) 1M acetic acid and 1M sodium acetate is the best buffer solution because these compounds are a weak acid and its conjugate base, which can resist changes in pH when combined in equal molar concentrations.
Step-by-step explanation:
When selecting the combination that would make the best buffer solution, one should look for a weak acid and its conjugate base in roughly equal concentrations. Among the provided options, d) 1M acetic acid, water, and 1M sodium acetate fits these criteria perfectly. Acetic acid (HC₂H₃O₂) is a weak acid, and sodium acetate (NaC₂H₃O₂) is its conjugate base.
When combined in equal molar concentrations, they create an effective buffer solution that can resist changes in pH when small amounts of acid or base are added. This is illustrated by the buffering capacity shown when 1.0 M solutions of acetic acid and sodium acetate are mixed, where the pH remains relatively stable even after the addition of a strong acid or base.