What is a solution called if it has a pH greater than 7?

A solution with a pH greater than 7 is classified as a base or alkaline. This designation indicates that the solution has a lower concentration of hydrogen ions (H+) compared to hydroxide ions (OH-). The pH scale ranges from 0 to 14, where values below 7 are considered acidic, 7 is neutral, and values above 7 indicate basicity.

Basic solutions are characterized by their ability to accept hydrogen ions or donate hydroxide ions in chemical reactions. Common examples of basic substances include sodium hydroxide and ammonia, which exhibit the properties associated with a high pH.

In the context of the other choices, acidic solutions have a pH below 7, neutral solutions maintain a balanced pH at exactly 7, and "dilute" refers to the concentration of a solution rather than its pH level. Thus, the option identifying a solution with a pH greater than 7 as a base or alkaline is correct.