Which of the following best indicates the highest acidity on the pH scale?

A pH of 1 represents the highest acidity on the pH scale, which ranges from 0 to 14. In this scale, lower pH values indicate higher concentrations of hydrogen ions (H+), which correspond to stronger acids. A pH of 1 is very acidic, often associated with strong acids like hydrochloric acid (HCl).

In contrast, a pH of 7 is considered neutral, meaning it has an equal concentration of hydrogen ions and hydroxide ions, such as pure water. A pH of 14 indicates a very basic or alkaline solution, where the concentration of hydroxide ions (OH-) is significantly higher than that of hydrogen ions. A pH of 10 is also mildly basic and farther away from the acidic range than a pH of 1. Therefore, the correct choice correctly identifies a pH level that is indicative of a very high acidity.