Which of the following molecular compounds is a nonelectrolyte and therefore does not conduct electricity in aqueous solution?

Introduction / Context:
Electrolytes are substances that produce ions when dissolved in water and thus conduct electricity in aqueous solution. Nonelectrolytes dissolve without forming ions and do not conduct electricity. Recognising which compounds behave as electrolytes or nonelectrolytes is important in chemistry, biology and many practical applications. This question asks you to identify a nonelectrolyte among a set of common substances.

Given Data / Assumptions:

• The compounds listed are C2H6O (ethanol), HCl, Na2CO3 and NaCl.
• We consider their behaviour when dissolved in water.
• An electrolyte forms ions in solution and allows electric current to pass.
• A nonelectrolyte remains as neutral molecules and does not conduct electricity significantly.

Concept / Approach:
Strong electrolytes include soluble ionic compounds such as sodium chloride and sodium carbonate, and strong acids such as hydrochloric acid. These dissociate almost completely into ions in water. Ethanol (C2H6O), on the other hand, is a covalent organic molecule that does not ionise significantly in water. It dissolves by forming hydrogen bonds with water but remains as neutral ethanol molecules. Because there are very few ions present, aqueous ethanol is essentially a nonelectrolyte and conducts electricity very poorly compared with ionic solutions.

Step-by-Step Solution:
Step 1: Classify each substance as ionic or molecular and as acid, base or neutral compound. Step 2: HCl is a strong acid that ionises in water to give H+ and Cl- ions, making it a strong electrolyte. Step 3: NaCl is an ionic salt that dissociates into Na+ and Cl- ions, also a strong electrolyte. Step 4: Na2CO3 is another ionic salt that dissociates into Na+ and CO3^2- ions in solution, again an electrolyte. Step 5: C2H6O (ethanol) is a covalent organic compound that dissolves in water as neutral molecules with negligible ionisation. Step 6: Because ethanol does not form ions in solution, it is a nonelectrolyte and does not conduct electricity significantly.

Verification / Alternative check:
Conductivity experiments with a simple circuit and a light bulb show that solutions of NaCl, Na2CO3 or HCl cause the bulb to glow brightly, indicating good conduction. In contrast, a solution of pure ethanol in water produces little or no glow, showing very low conductivity. Textbooks on chemistry list ethanol and most other simple alcohols as nonelectrolytes, while strong acids and soluble ionic compounds are consistently listed as strong electrolytes.

Why Other Options Are Wrong:
HCl: This is a strong acid that ionises completely in water, making it a strong electrolyte, not a nonelectrolyte.

Na2CO3: This is a salt composed of Na+ and CO3^2- ions, which dissociate in solution and conduct electricity well.

NaCl: This is a common table salt that dissociates into Na+ and Cl- ions and is a classic example of an electrolyte.

Common Pitfalls:
Some learners mistakenly assume that any substance that dissolves in water is an electrolyte. In reality, many organic molecules like sugars and alcohols dissolve readily but do not ionise, so they do not conduct electricity. Others may be misled by the fact that ethanol can burn and has chemical energy, but this has nothing to do with ionic conduction. Always check whether the compound forms ions in solution when deciding if it is an electrolyte.

Final Answer:
Among the given compounds, C2H6O (ethanol) is a nonelectrolyte and does not conduct electricity significantly in aqueous solution.