Metallic Solids – Copper as a Monoatomic Solid Assertion (A): Copper is a monoatomic solid. Reason (R): In metals, the valence electrons are delocalized and belong to all atoms (electron gas model).

Introduction / Context:
Crystalline solids are described by a lattice and a basis. A “monoatomic” solid has one atom in the basis of its Bravais lattice (for copper, face-centered cubic with a single-atom basis). Metals also exhibit metallic bonding, where valence electrons are delocalized. This question separates structural classification from bonding description.

Given Data / Assumptions:

• Copper crystallizes in an fcc structure with one atom per lattice point.
• Metallic bonding is characterized by delocalized conduction electrons.
• Room-temperature crystalline state considered.

Concept / Approach:

The statement “monoatomic solid” concerns the crystal basis, not the bonding mechanism. Copper’s fcc lattice indeed has a single-atom basis, so A is true. The reason describes electron delocalization which explains metallic conductivity and cohesion, but it does not logically explain why copper is “monoatomic” in the crystallographic sense; bonding type does not determine the number of atoms in the basis.

Step-by-Step Solution:

Verification / Alternative check:

X-ray diffraction shows fcc reflections consistent with a single-atom basis; conductivity and cohesive properties align with delocalized electron gas theory but are independent of the basis count.

Why Other Options Are Wrong:

• A true, R false: R is not false; metals do have delocalized electrons.
• R explaining A: incorrect causal link; crystal basis is not determined by electron delocalization.
• A false: Copper is not molecular or polyatomic in its crystal basis.

Common Pitfalls:

Equating bonding type with lattice basis; thinking “monoatomic” refers to monoatomic gases rather than crystal basis.

Final Answer:

Both A and R are true but R is not correct explanation of A