Take solutions of glucose, alcohol, hydrochloric acid, sulphuric acid, etc.Fix two nails on a cork, and place the cork in a 100 mL beaker.Connect the nails to the two terminals of a 6 volt battery through a bulb and a switch, as shown in figure.Now pour some glucose solution in the beaker and switch on the current.Repeat with alcohol solution and hydrochloric acid.

It is observed that bulb does not glow using glucose or alcohol solution. While if a solution of acid is used instead of glucose or alcohol solution, bulb glows.

Bulb glows when the solution of hydrochloric acid is used, because it dissociates hydronium ion in aqueous solution. But glucose and alcohol do not dissociate hydronium ion in the water, which is responsible for the conduction of electricity. Hence solution of glucose and alcohol do not conduct electricity.