Which of the following is true about the pH scale? Group of answer choices A pH of 9 has a greater concentration of hydrogen ions (H+1) than pH 7. At pH 7 the hydrogen ion (H+1) concentration is equal to the hydroxide ion concentration (OH-1). At pH 7 there are no hydroxide ions (OH-1). A pH of 4 has a greater concentration of hydroxide ions (OH-1) than pH 7. At pH 7 there are no hydrogen ions (H+1).