A solution with a pH of 7 has a [OH1-] of?

Question

0M or 7M???????????????????

Answer 1

Neither.
pH + pOH = pKw = 14.
You know pH and pKw, solve for pOH.
Then pOH = -log(OH^-). Solve for OH^-

You can do this another way and get the same answer.
pH = -log(H^+). Substitute pH and solve for (H^+), then
(H^+)(OH^-) = Kw = 1E-14. You know H^+) and Kw, solve for OH^-