Final answer:
The Arrhenius definition of a base is a substance that increases the concentration of hydroxide ions (OH-) in aqueous solution, making it more basic. The correct answer is A substance that increases OH– concentration when it is dissolved in water.
Step-by-step explanation:
The Arrhenius definition of a base is a substance that increases the concentration of hydroxide ions (OH−) in aqueous solution. When a substance that is an Arrhenius base dissolves in water, it produces hydroxide ions which make the solution more basic.
This is different from an Arrhenius acid, which increases the concentration of hydrogen ions (H+), or more precisely, hydronium ions (H3O+), making the solution more acidic. A classic example of an Arrhenius base is sodium hydroxide (NaOH), which dissociates in water to produce sodium ions (Na+) and hydroxide ions (OH−).