To identify which solution is a base, we can refer to the pH scale. A pH less than 7 indicates acidity, a pH of 7 is neutral, and a pH greater than 7 indicates alkalinity (basicity).
Given the pH values:
- Solution A: pH 2 (acidic)
- Solution B: pH 5 (acidic)
- Solution C: pH 7 (neutral)
- Solution D: pH 9 (basic)
Based on this information, Solution D (with a pH of 9) should be identified as being a base.