Among crystalline solids, which type typically conducts electricity well in the solid state?

• A. Ionic Solids
• B. Molecular Solids
• C. Metallic Solids
• D. Covalent-network Solids

Answer: (C)

Electrical conductivity in crystalline solids depends on whether charge carriers can move freely through the material. In metallic solids, atoms form a lattice with a sea of delocalized electrons not bound to any specific atom. These electrons can flow under an applied electric field, giving metals their high conductivity in the solid state. This free-electron behavior comes from metallic bonding and overlapping energy bands that place available states near the Fermi level for electrons to occupy and move.

Ionic solids have ions fixed in a lattice, so there are no mobile charge carriers in the solid form; conductivity is essentially negligible unless the material is molten or dissolved. Molecular solids consist of discrete molecules held together by weaker forces, so there are no freely moving charges in the solid. Covalent-network solids have electrons tied up in strong covalent bonds across an extended network, leaving few free carriers for conduction (with rare exceptions like graphite, where delocalized electrons exist along planes).

Thus the type that typically conducts electricity well in the solid state is metallic solids.