What is most likely the pH of a solution containing many hydroxide ions (OH-) and few hydrogen ions (H+)?

The pH of a solution is determined by the concentration of hydrogen ions (H+) it contains. A solution that has many hydroxide ions (OH-) and only a few hydrogen ions is likely to be basic or alkaline. The presence of hydroxide ions indicates that the solution can neutralize acids and will typically have a pH greater than 7.

The pH scale ranges from 0 to 14, with 7 being neutral. As the pH increases above 7, the concentration of hydroxide ions increases relative to hydrogen ions, leading to a more basic solution. A pH of 9 indicates a moderately alkaline solution, which aligns well with having a higher concentration of hydroxide ions compared to hydrogen ions.

A pH close to 13 represents a strongly basic solution, which might also seem plausible given the high number of hydroxide ions; however, a pH of 9 is a more common indicator of basicity with a reasonable imbalance where there are still some hydrogen ions present. Therefore, 9 is more likely associated with a solution that still retains some acidity but leans toward the basic side, making it the most reasonable choice in this context.