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. Recall the definition of an Arrhenius base: a substance that increases the concentration of hydroxide ions (OH\(\textsuperscript{-}\)) when dissolved in water.
2. Examine each option to see if it produces OH\(\textsuperscript{-}\) ions in aqueous solution:
3. a) Mg(OH)\(\textsubscript{2}\) dissociates in water to give Mg\(\textsuperscript{2+}\) and 2 OH\(\textsuperscript{-}\) ions, so it fits the Arrhenius base definition.
4. b) BaO reacts with water to form Ba(OH)\(\textsubscript{2}\), which then dissociates to give OH\(\textsuperscript{-}\) ions, so BaO is also an Arrhenius base.
5. c) CH\(\textsubscript{3}\)NH\(\textsubscript{2}\) is a base but it does not produce OH\(\textsuperscript{-}\) directly; it is a Brønsted-Lowry base, not an Arrhenius base.