Which of the following is an Arrhenius base?

• A. Mg(OH)₂
• B. BaO
• C. CH₃NH₂
• D. NH₄⁺
• E. H₂SO₄

Answer: (A)

Verified step by step guidance

1. Understand the definition of an Arrhenius base: An Arrhenius base is a substance that increases the concentration of hydroxide ions (OH^-) when dissolved in water.
2. Analyze each option to determine if it fits the definition of an Arrhenius base.
3. Option a) Mg(OH)₂: When dissolved in water, it dissociates to produce Mg²⁺ and 2 OH^- ions, thus increasing the concentration of hydroxide ions.
4. Option b) BaO: Reacts with water to form Ba(OH)₂, which then dissociates to produce Ba²⁺ and 2 OH^- ions, increasing the concentration of hydroxide ions.
5. Evaluate the remaining options: c) CH₃NH₂ is a weak base but not an Arrhenius base, d) NH₄⁺ is an acid, and e) H₂SO₄ is an Arrhenius acid, not a base.