What defines metallic solids?

Metallic solids are characterized by a unique arrangement and bonding of metal atoms, which influences their properties significantly. They are made up of metal atoms that are arranged in a regular pattern, forming a lattice structure. This arrangement allows for a strong interaction between the positively charged metal ions and the delocalized electrons that can move freely throughout the structure.

The presence of these delocalized electrons is a key aspect of metallic solids, contributing to their electrical and thermal conductivity. The clustering of metal atoms in a repeating unit leads to the typical properties associated with metals, including high density and the ability to maintain structural integrity under various conditions.

In contrast, ionic bonds, which involve the electrostatic attraction between cations and anions, do not define metallic solids. The absence of free-moving electrons and the softness and malleability stated in the other choices do not capture the essence of metallic structures. Instead, the basis of their properties is deeply tied to the presence of metal atoms organized in a lattice with mobile electrons around them. Thus, the correct answer accurately reflects the comprehensive understanding of the structure and characteristics of metallic solids.