A solution is found to contain 1 x 10-4 OH− ions, determine the pH of this solution.

I did this problem and got 4 but it is not going in as correct.

-log(1*10^-4)=4

3 answers

It is; however, your calculation gives you pOH. If you want pH, use
pH + pOH = pKw = 14 and solve for pH.

Or you can use (H^+)(OH^-) = Kw = 1E-14

pH = -log(H^+)
pOH = - log(OH^-)
I did it and got 10 and it is saying that its incorrect
pOH = 4
pH = 10

Or
(H^+) = 1E-14/1E-4 = 1E-10
pH = 10
The data base is wrong or you posted the problem incorrectly. The pH is 10 for the above problem.