Pure crystals of the metallic element copper are composed of which of the following structural units?

Molecules consist of two or more atoms that are chemically bonded together, typically involving nonmetals. Since copper is a pure metallic element, it does not form molecular structures; rather, it exists as individual atoms in a lattice. Therefore, the concept of molecules does not apply to pure copper crystals.

Compounds are substances formed from two or more different elements that are chemically combined in fixed proportions. Pure copper does not consist of different elements; it is a single element with no chemical combination occurring. Thus, it cannot be classified as a compound.

Ions are charged particles that result from the loss or gain of electrons from atoms. While copper can exist in ionic form (such as Cu²⁺ in compounds), pure copper crystals are not composed of ions; they are composed of neutral copper atoms. Consequently, this option does not accurately describe the structural units of pure copper.