Which of the soutions would have the HIGHEST hydrogen ion concentration?

Solution with a pH = 1

Solution with a pH = 12

Solution with a pH = 7

Solution with a pH = 9

Solution with a pH = 5

Solution with a pH = 1

Explanation:

So the pH equation is pH = -log[H+]. To get the [H+] (hydrogen ion concentration), you rearrange to get [H+] = 10^-pH.

Solution with a pH = 1 ,  [H+] = .1 M

Solution with a pH = 12 , [H+] = 1*10^-12 M

Solution with a pH = 7 ,  [H+] = 1*10^-7 M

Solution with a pH = 9 ,  [H+] = 1*10^-9 M

Solution with a pH = 5,  [H+] = 1*10^-5 M

Another way to get the a high hydrogen ion concentration means that the solution should be more acidic. The most acidic pH of the 5 solutions is the one with a pH = 1.