Which type of solution has a pH level lower than 7?

An acidic solution is characterized by a pH level lower than 7. The pH scale ranges from 0 to 14, where a pH of 7 is considered neutral, indicating a balance between hydrogen ions (H⁺) and hydroxide ions (OH⁻). When the pH falls below 7, this indicates a higher concentration of hydrogen ions compared to hydroxide ions, which is a defining property of acidic solutions.

In contrast, a neutral solution has a pH of exactly 7, indicating neither acidity nor basicity. Basic solutions have a pH greater than 7, reflecting a higher concentration of hydroxide ions compared to hydrogen ions. Buffer solutions are designed to maintain a constant pH when small amounts of acids or bases are added and can be acidic or basic depending on their specific composition, but they do not inherently define acidity or basicity by themselves without considering their specific pH. Thus, among these options, the acidic solution is distinctively the one that consistently has a pH lower than 7.