Answer: Increasing the pH from 5 to pH 8 corresponds to a 1,000-fold decrease in hydrogen ion concentration and makes the treated pond water 1,000 times more alkaline.
B 1,000
Explanation: The pH scale is logarithmic, meaning that each whole number change in pH represents a tenfold change in hydrogen ion concentration. Since the pH increased from 5 to 8, it means that the hydrogen ion concentration decreased by a factor of 10 raised to the power of (8-5), which is 1,000.