Final answer:
Water is not an element because it can be decomposed into simpler substances, hydrogen and oxygen, which are gases. Pure water is an insulator due to the immobility of ions, while a solution with dissolved ionic compounds is a conductor because of the free-moving ions that enable current flow.
Step-by-step explanation:
When an electric current is passed through water, two gases, hydrogen and oxygen, can be collected. This demonstrates that water is not an element because it can be chemically split into simpler substances, contradicting the definition of an element as a substance that cannot be broken down into simpler substances chemically. Insulators, like pure water and dry table salt, have bound electrons and ions that move very slowly compared to conductors. However, when certain compounds like salt are dissolved in water, the solution becomes a conductor due to the mobility of ions, as shown in conductivity experiments.
Substances that allow the free movement of ions in solution are known as electrolytes. Water itself, without any dissolved ionic compounds, is a poor conductor with a low concentration of ions, making it an electrical nonconductor. It becomes a conductor only when ionic compounds are dissolved in it, creating a solution where positive and negative ions are free to move, which enables an electric current to flow through the solution.