If [oh-] = 1×10_4, what is the ph of the solution

If the hydrogen ion concentration of a solution is 10–10M, is the solution is definitely alkaline. The thing I used to determine that fact is a basic point  - pH above 7 is always alkaline, and as a proof, we can see from the task that the concentration of hydroxyl OH- is pretty higher than hydrogen H+, which is a direct characteristic of the alkain solution.Here is a tip for you, I bet it will be useful : >7 = basic <7 = acidic 7 = neutral

They are all decomposition reactions.