Electrical conductivity in solutions depends on the presence of free-moving charged particles, which are typically ions. Substances that dissolve in water to produce ions are called electrolytes. These solutions can conduct electricity. Substances that dissolve in water but do not produce ions are called non-electrolytes. Their solutions do not conduct electricity.

Understanding Electrical Conductivity in Solutions

When ionic compounds dissolve in water, their ions separate and become mobile. For example, sodium chloride (NaCl) dissociates into sodium ions (Na⁺) and chloride ions (Cl^-) in water. These free ions can move towards electrodes when an electric field is applied, carrying the electric current through the solution.

Similarly, copper sulphate (CuSO₄) dissolves to form copper ions (Cu²⁺) and sulphate ions (SO₄^2-), and sodium hydroxide (NaOH) dissolves to form sodium ions (Na⁺) and hydroxide ions (OH^-). The presence of these ions allows their solutions to conduct electricity.

Analyzing the Options for Conductivity

• Copper sulphate solution: Copper sulphate (CuSO₄) is an ionic compound. In water, it dissociates into Cu²⁺ and SO₄^2- ions. These ions are free to move, making the solution capable of conducting electricity.
• Sodium chloride solution: Sodium chloride (NaCl) is a common salt and an ionic compound. In water, it dissociates into Na⁺ and Cl^- ions. The presence of these ions allows the solution to conduct electricity.
• Sugar solution: Sugar, typically sucrose (C₁₂H₂₂O₁₁), is a covalent compound. When sugar dissolves in water, its molecules separate but do not break down into ions. The dissolved sugar exists as neutral molecules. Since there are no free-moving ions or charged particles, a sugar solution cannot conduct electricity.
• Sodium hydroxide solution: Sodium hydroxide (NaOH) is a strong base and an ionic compound. In water, it dissociates into Na⁺ and OH^- ions. These ions are free to move, making the solution capable of conducting electricity.

Based on the analysis, sugar solution is the only one among the given options that does not produce free ions when dissolved in water, and therefore, it is not capable of conducting electricity.

Revision Table: Key Concepts

Additional Information on Solution Conductivity

The ability of a solution to conduct electricity is also influenced by the concentration of ions and the temperature. Higher concentration of ions generally leads to higher conductivity, assuming complete dissociation. Temperature affects the mobility of ions; generally, conductivity increases with temperature due to increased kinetic energy and reduced viscosity of the solvent.

Acids and bases, besides salts, can also form electrolytic solutions because they produce ions (H⁺ or H₃O⁺, and OH^- respectively) when dissolved in water.

Pure water itself has very low conductivity because it contains very few ions formed by self-ionization. Dissolving even small amounts of ionic substances significantly increases its conductivity.