Final answer:
Moving from a pH of 4 to a pH of 9 indicates a solution that is 100,000 times less acidic since pH levels are on a logarithmic scale.
Step-by-step explanation:
When discussing pH levels, we are dealing with a logarithmic scale that represents the concentration of hydrogen ions in a solution. Each whole number change in pH represents a tenfold change in hydrogen ion concentration. Therefore, moving from a pH of 4 to a pH of 9 is not a simple linear transition but rather represents a change by a factor of 105 (10 x 10 x 10 x 10 x 10), or 100,000 times. This means that a solution with a pH of 9 is 100,000 times less acidic (or more basic) than a solution with a pH of 4.