What is a concentrated base?

• A. A base that contains a large number of OH- ions
• B. A base that has high pH but few ions
• C. A base with low solute concentration
• D. A base that does not ionise in solution

Answer: (A)

Concentration is about how much dissolved material there is in a given volume. In water, bases produce hydroxide ions (OH−). So a concentrated base means there are many OH− ions present per unit volume of solution. The statement that a base contains a large number of OH− ions directly describes this high concentration of the basic species in solution, which is what “concentrated” means. The other ideas describe either few ions despite a high pH, or a dilute amount of solute, or no ionisation at all, none of which match the idea of a concentrated base.