One way in which chemists try to understand substances is to observe their properties and to classify the substances based on their properties.
Broadly substances can be classified as pure substances or mixtures.
Homogeneous mixtures are uniform throughout.
Solutions are homogeneous mixtures. A solution is a mixture of a solute (often solid) dissolved in a solvent (often liquid).
Water is an important solvent.
Solutions in which water is the solvent are referred to as aqueous solutions.
Classifying solutes
Solutes can be classified as electrolytes or non-electrolytes depending on the conductivity of their aqueous solution.
Substances giving rise to charged particles on dissolving in water are classed as electrolytes.
Ionic solids are electrolytes because to the extent that they dissolve, they dissociate into ions.
Broadly substances can be classified as pure substances or mixtures.
Homogeneous mixtures are uniform throughout.
Solutions are homogeneous mixtures. A solution is a mixture of a solute (often solid) dissolved in a solvent (often liquid).
Solutions of solids in liquids are clear (transparent). Their colour depends on the solute; many solutions are colourless.
The solution of water and the blue solid copper sulfate is blue.
The solution of water and the blue solid copper sulfate is blue.
Water is an important solvent.
Solutions in which water is the solvent are referred to as aqueous solutions.
Classifying solutes
Solutes can be classified as electrolytes or non-electrolytes depending on the conductivity of their aqueous solution.
Substances giving rise to charged particles on dissolving in water are classed as electrolytes.
Ionic solids are electrolytes because to the extent that they dissolve, they dissociate into ions.
NaCl(s) 
Na+(aq) + Cl–(aq)
Electrical current is movement of charge, and the ions can move in the solution to complete an electrical circuit. Na+(aq) + Cl–(aq)