From the point of view of atomic structure, which of the following is the main reason why metallic solids are good conductors of electricity?

Introduction / Context:
Metals are widely used in electrical wiring and electronic components because they conduct electricity very well. This good conductivity is closely tied to the internal structure of metals at the atomic and electronic level. The question asks you to identify the primary reason that explains why metals allow electric current to flow so easily.

Given Data / Assumptions:

• We are considering metallic solids such as copper, aluminium, and silver.
• Electricity conduction refers to the movement of electric charge through the metal.
• Several material properties are proposed as possible reasons.

Concept / Approach:
In metallic bonding, atoms in the metal lattice contribute some of their outer electrons to form a sea of delocalised or free electrons that can move throughout the crystal. These mobile electrons act as charge carriers when a potential difference is applied, resulting in electric current. Properties such as melting point, tensile strength, or atomic density may influence other characteristics, but they are not the fundamental cause of electrical conductivity in metals.

Step-by-Step Solution:
Step 1: Recall that electric current in a metal is due to the motion of electrons. Step 2: In metals, the outer electrons are not tightly bound to individual atoms and can move relatively freely. Step 3: When a voltage is applied across a metal, these free electrons drift in a preferred direction, forming an electric current. Step 4: Thus, the key reason for good conductivity is the presence of many free or delocalised electrons, not properties like melting point or tensile strength.

Verification / Alternative check:
Non-metals, such as rubber or glass, do not have a comparable sea of free electrons and are typically insulators. Alloys or materials with fewer free electrons have lower conductivity. This contrast supports the idea that mobile electrons are the crucial factor. Experiments on temperature dependence of resistance in metals also show behaviour that fits the free electron model.

Why Other Options Are Wrong:

• Because they have a low melting point: Many metals, like iron and tungsten, have high melting points yet conduct electricity well. Melting point is not the key factor for conduction.
• Because they have high tensile strength: Tensile strength measures resistance to pulling forces and is mainly mechanical, not directly related to electrical conductivity.
• Because they have very high atomic density: While metals often have closely packed atoms, high density alone does not guarantee good electrical conduction. Some dense materials are poor conductors.

Common Pitfalls:
Students sometimes mix up physical properties and assume that any strong or dense material must be a good conductor. Another confusion is thinking that ions, rather than electrons, carry current in metals. In metallic solids, conduction is dominated by electrons, while ionic conduction is more relevant in solutions and molten salts. Always link metallic conductivity to the presence of free electrons.

Final Answer:
Metals conduct electricity mainly because they contain many free electrons.