Which of the following substances will become completely dissociated when dissolved in water?

• A. NaCl
• B. CH3COOH
• C. NH3
• D. H2CO3

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the concept of dissociation in water. When ionic compounds dissolve in water, they often dissociate completely into their constituent ions. However, molecular compounds, especially weak acids and bases, may only partially dissociate.
2. Step 2: Identify the nature of each substance: NaCl is an ionic compound (a salt), CH3COOH (acetic acid) is a weak acid, NH3 (ammonia) is a weak base, and H2CO3 (carbonic acid) is a weak acid.
3. Step 3: Recall that strong electrolytes like NaCl dissociate completely in water, meaning NaCl separates fully into Na⁺ and Cl⁻ ions.
4. Step 4: Recognize that weak acids and bases such as CH3COOH, NH3, and H2CO3 only partially ionize in water, establishing an equilibrium between the undissociated molecules and ions.
5. Step 5: Conclude that among the given substances, only NaCl will become completely dissociated when dissolved in water.