Which of the following is correct regarding the pH scale?
a. A substance with pH of 3 is 10 times as acidic as substance with PH of 4.
b. A substance with pH of 3 is twice as alkaline as substance with pH of 4.
c. A substance with pH of 3 is twice as acidic as substance with a pH of 4.
d. A substance with a pH of 3 is 10 times as alkaline as substance with PH of4.