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?

Pure water is neutral, so its pH is about 7 before anything is added. Sodium hydroxide is a base; adding it makes the solution more alkaline and raises its pH above 7. Therefore, the most likely values are 7 before and 9 after, choice A.

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