Which of the following statements is true for strong electrolytes?

Analysis

The question asks for the defining characteristic of a strong electrolyte. To answer this, we must distinguish between how different substances behave when dissolved in water or melted.

Concept Explanation

An electrolyte is a substance that produces an electrically conducting solution when dissolved in a polar solvent (like water) or when melted.

• Strong Electrolytes: These are substances that undergo complete ionization or complete dissociation when dissolved in water. Because they break down entirely into free-moving ions, they are excellent conductors of electricity. Examples include strong acids (like $HCl$), strong bases (like $NaOH$), and soluble salts (like $NaCl$).
• Weak Electrolytes: These substances only partially dissociate into ions in solution. They exist in equilibrium between the undissociated molecules and the ions. Examples include weak acids (like acetic acid) and weak bases (like ammonia).
• Non-electrolytes: These do not dissociate into ions at all (e.g., sugar or ethanol) and therefore do not conduct electricity.

Step-by-Step Solution

1. Evaluate Option A: Strong electrolytes are ionic compounds. In the molten state, their crystal lattice breaks down, allowing ions to move freely. Therefore, they do conduct electricity when molten. This statement is false.
2. Evaluate Option B: By definition, a strong electrolyte dissociates completely into its constituent ions in solution. This provides a high concentration of charge carriers, making the solution a strong conductor. This statement is true.
3. Evaluate Option C: Strong electrolytes are typically ionic compounds, which are highly polar. Non-polar substances (like oil or benzene) generally do not conduct electricity. This statement is false.
4. Evaluate Option D: Partial dissociation is the characteristic of weak electrolytes, not strong ones. This statement is false.

Conclusion

Based on the principles of electrochemistry, strong electrolytes are defined by their ability to ionize completely in solution.

Exam Tip: Remember the "Strong/Weak" rule: Strong = Complete dissociation; Weak = Partial dissociation. If you see "completely," think "strong"; if you see "partially," think "weak."