Which pH level signifies that a solution is very weakly basic?

A pH level of 9 indicates that a solution is very weakly basic. The pH scale ranges from 0 to 14, where a pH of 7 is considered neutral. Values below 7 indicate acidity, while values above 7 indicate basicity.

At a pH of 9, the concentration of hydroxide ions is greater than the concentration of hydrogen ions, but the solution is still only slightly basic compared to higher pH values. For example, a pH of 12 would denote a much stronger basicity due to a significantly higher concentration of hydroxide ions. On the other hand, a pH of 5 or 6 would indicate slightly acidic to neutral conditions, which do not represent basic conditions at all.

Thus, a pH of 9 effectively signifies a very weakly basic solution, making it the correct choice in this context.