Final answer:
A pH less than 5.5 indicates an acidic solution, with a higher concentration of hydronium ions compared to neutral water, and the further below 7 the pH value is, the greater the acidity.
Step-by-step explanation:
If the pH is less than 5.5, it indicates that the solution is acidic. On the pH scale, which ranges from 0 to 14, a pH value below 7 signals acidity. This means the solution has a higher concentration of hydronium ions (H₃O+) relative to pure water (which has a pH of 7 and is considered neutral). For example, gastric juices in the stomach have a low pH, which is crucial for the digestion of food, but too low of a pH can be damaging to organisms and materials. The lower the pH value below 7, the greater the acidity and the higher the concentration of hydronium ions in the solution.