Acids and bases are the property of the solution based on the concentration of the ions. Solution IV is the most concentrated base as it has the highest concentration of hydroxide ions.
Bases are substances or solution that has the potential of hydrogen above 7 on the pH meter scale. It has more hydroxide ions than hydronium or hydrogen ions.
The higher the hydroxide concentration lower will be the pOH and the more alkaline will be the solution. The hydroxide ions have more electrons and can donate some to other species.
Therefore, solution IV is a concentrated base because of high hydroxide ion concentrations.
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