Sodium hydroxide (naoh) was added to pure water (h2o). which most likely were the ph values of the water before and after the sodium hydroxide was added to it?
before = 7, after = 9
before = 7, after = 4
before = 4, after = 7
before = 9, after = 7

The most likely pH vale of water before was 7 and after the addition of sodium hydroxide the pH value of water becomes 9. So the correct option among all the options that are given in the question is the first option. Sodium hydroxide is a strong base and so on adding it to neutral water, the solution becomes basic in nature.

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