The atomic number of H2O is 18 hence it contains 18 protons. Hope this helps.
Answer:
0.805 M.
Explanation:
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In this case, since the molarity of a solution is computing by dividing the moles of solute over the volume of solution in liters (M=n/V), for 15.0 g of potassium chloride (74.55 g/mol) we compute the corresponding moles:

Next, since the volume is 0.2500 in liters, the molarity turns out:

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The answer to your question is letter A! Hope that helps