ACS Chemistry Practice Exam 2025 – The All-in-One Guide to Exam Success!

When solid ionic compounds are fused, they exhibit high conductivity due to the process of melting, which transforms the solid ionic lattice into a liquid state. In a solid state, ions are fixed in place within the crystalline structure and cannot move freely, which restricts electrical conductivity. However, when the ionic compound is heated to its melting point, the rigid lattice structure breaks down, allowing the ions to become mobile.

In this liquid state, these charged ions can move freely and carry electric current, leading to high conductivity. This property of ionic compounds is largely due to their ability to dissociate into their constituent ions when melted or dissolved in a solvent, such as water.

The incorrect options reflect states where the ionic compounds are not able to conduct electricity effectively. Solid ionic compounds typically have either low or no conductivity, as the ions are locked in place. In contrast, once fused, the mobility of the ions is what allows for the high conductivity characteristic of molten ionic compounds.