All of the following can be used to define an acid except

a hydrogen ion donor in a reaction

a substance that increases the hydronium ion concentration of a solution

an electron-pair acceptor in a reaction

a substance that increases the hydroxide ion concentration of a solution

I think the correct answer from the choices listed above is the last option. All of the following can be used to define an acid except the statement that it is a substance that increases the hydroxide ion concentration of a solution. Instead, it is a substance that increases hydrogen ion concentration.