Correct Response: C. The pH of a solution is measured using a logarithmic scale. A logarithm is an exponent. This means that each whole number value on the pH scale is 10 times more acidic than the next greater whole number value. Since a pH of 6 is greater than a pH of 3 by 3 whole number values, a pH of 3 is 1000x (10 x 10 x 10 = 10 3 ) more acidic than a pH of 6. (A) incorrectly assumes that the relationship is multiplicative instead of logarithmic (2 x 3 = 6). (B) represents the difference in acidity between two consecutive whole number values on the pH scale. (D) represents a combination of a multiplicative and logarithmic relationship between whole number values on the pH scale (2 x 10 x 10 x 10).
