If the pH of a Ca(OH)2 solution is measured as 9.0, what is the concentration of the Ca(OH)2 solution?

A. 1 * 10^-5 M
B. 1 * 10^-8 M
C. 1 * 10^-9 M
D. 1 * 10^-6 M

I really have no clue

2 answers

pH=-log(H)
H=10^-9
but OH*H=10^-14
OH=10^-5
Thank you!!!