ANS:C - 1000

The pH scale is a logarithmic scale that measures the concentration of hydrogen ions (𝐻+H+) in a solution. A decrease in pH value indicates an increase in the concentration of hydrogen ions. The relationship between pH and hydrogen ion concentration can be expressed by the equation: pH=−log⁡[𝐻+]pH=−log[H+] Therefore, a change in pH from 5 to 2 indicates a decrease in pH by 3 units. This corresponds to an increase in the hydrogen ion concentration by a factor of 103103, since each unit change in pH represents a tenfold change in hydrogen ion concentration. So, the increase in hydrogen ion concentration is 103103 times. Therefore, the correct option is 1000.