Which of the following equations shows the complete dissociation of a strong base in water?

• A. NH_3(aq) + H_2O(l) ightarrow NH_4^+(aq) + OH^-(aq)
• B. Ca(OH)_2(s) ightarrow Ca(OH)_2(aq)
• C. KOH(aq) ightarrow KOH(s)
• D. NaOH(s) ightarrow Na^+(aq) + OH^-(aq)

Answer: (D)

Verified step by step guidance

1. Step 1: Understand what complete dissociation means for a strong base in water. A strong base dissociates fully into its ions when dissolved in water, meaning it separates entirely into cations and hydroxide ions (OH⁻).
2. Step 2: Analyze each given equation to see if it represents a strong base fully dissociating into ions in aqueous solution. The equation should show the base in aqueous form (dissolved in water) and breaking down into its ions.
3. Step 3: For example, the equation for sodium hydroxide (NaOH) should be written as \(\mathrm{NaOH(aq) \rightarrow Na^{+}(aq) + OH^{-}(aq)}\), indicating it is dissolved in water and dissociates completely.
4. Step 4: Identify incorrect options: equations showing solids without dissolution, or weak bases like ammonia (NH₃) which do not fully dissociate, are not correct representations of complete dissociation.
5. Step 5: Conclude that the correct equation must show the strong base in aqueous form dissociating fully into its ions, such as \(\mathrm{NaOH(s) \rightarrow Na^{+}(aq) + OH^{-}(aq)}\) after dissolution, but properly written with (aq) on the reactant side to indicate it is dissolved.