One solution turns blue. A possible hydrogen ion concentration for this solution is:
1x 10-2 M.
5x 10-2 M
5 x 10 M
1x 10-8 M

1x10^-8 M

Explanation:

Since the solution turns blue, it mean the solution is a base.

Now, to know which option is correct, we need to determine the pH of each solution. This is illustrated below:

1. Concentration of Hydrogen ion, [H+] = 1x10^-2 M

pH =..?

pH = - log [H+]

pH = - log 1x10^-2

pH = 2

2. Concentration of Hydrogen ion, [H+] = 5x10-2 M

pH =..?

pH = - log [H+]

pH = - log 5x10^-2

pH = 1.3

3. Concentration of Hydrogen ion, [H+] = 5x10 M

pH =..?

pH = - log [H+]

pH = - log 5x10

pH = - 1.7

4. Concentration of Hydrogen ion, [H+] = 1x10-8 M

pH =..?

pH = - log [H+]

pH = - log 1x10^-8

pH = 8

A pH reading shows if the solution is acidic or basic. A pH reading between 0 and 6 indicates an acidic solution, a pH reading of 7 indicates a neutral solution while a pH reading between 8 and 14 indicates a basic solution.

From the above calculations, the pH reading indicates a basic solution when the hydrogen ion concentration was 1x10^-8 M.