Final answer:
Ammonium hydroxide (NH4OH) is the Arrhenius base among the given options as it dissociates to yield hydroxide ions (OH−) when dissolved in aqueous solution.
Step-by-step explanation:
According to the Arrhenius definition, an Arrhenius base is a substance that dissociates in water to yield hydroxide ions (OH−). From the given options Ammonium hydroxide (NH4OH) is an Arrhenius base. When ammonium hydroxide is dissolved in water, it dissociates as follows:
NH4OH(aq) → NH4+ (aq) + OH− (aq)
This reaction shows that ammonium hydroxide releases hydroxide ions into the solution, which is the characteristic property of an Arrhenius base. Therefore, the correct answer is b) Ammonium hydroxide (NH4OH).