Step 1: A solution conducts electricity only if it contains free ions that can carry charge. Step 2: Common salt (NaCl) dissolves in water and splits into Na⁺ and Cl⁻ ions, so the solution conducts and the bulb glows. Step 3: Sugar and alcohol dissolve as neutral molecules and produce no ions. Distilled water has almost no ions. So the bulb does not glow in these. Step 4: Lemon juice, vinegar and acids also conduct, because they produce ions. Answer: Common salt solution.