Which solution has the greatest number of hydroxide ions? baking soda, ph = 9milk, ph = 6tomato juice, ph = 3.5vinegar, ph = 2

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Baking soda having a pH of 9, has the maximum number of hydroxide ions.

Explanation: -

More the pH of a solution, the more basic it is and more the number of hydroxide ions it has.

From the question we find that

baking soda has a pH = 9

milk has a pH = 6

tomato juice has a pH = 3.5

vinegar has a pH = 2

Thus among them baking soda has the highest pH.

So baking soda is the most basic and has the maximum number of hydroxide ions.