Which of the following solids act as electrical insulators in the solid state but become good conduc — Solid State Chemistry Question

💡 Solution & Explanation

Ionic solids like $NaCl$, $MgO$, and $CaF_2$ have their constituent ions fixed in lattice positions in the solid state, preventing electrical conduction. When melted or dissolved, these ions become free to move, allowing them to conduct electricity. $Fe$ is a metallic solid and conducts in both solid and molten states.