Final answer:
Acids are substances with a pH below 7, indicating a higher concentration of hydrogen ions and thus greater acidity compared to pure water.Correct answer is option A.
Step-by-step explanation:
Among the given options, A) They have a pH below 7 is true for acids. Acids are substances that have a higher concentration of hydronium ions (H+) compared to pure water. The pH scale, which ranges from 0 to 14, is used to measure the acidity or alkalinity of a solution.
Acids will have a pH value below 7, with the strength of an acid being indicated by how much lower its pH is than 7. The lower the pH, the higher the acidity, which means a greater concentration of hydrogen ions. Additionally, acids typically have a sour taste and can be harmful to organisms and materials if they are strong.