Metallic lustre is explained by

Options

A. Diffusion of metal ions
B. Oscillation of loose electrons
C. Excitation of free protons
D. Existence of bcc lattice

Explanation

To explain why metals exhibit metallic luster, we can break down the explanation into several steps:

### Step-by-Step Solution:

1. **Understanding Metallic Luster**:
- Metallic luster refers to the shiny appearance of metals. This property is characteristic of metals like sodium, aluminum, and gold.

2. **Role of Electrons**:
- Metals have loosely bound electrons, often referred to as "free electrons." These electrons are not tightly held by the nucleus and can move freely within the metal structure.

3. **Energy Level Transitions**:
- When light strikes the surface of a metal, these free electrons can absorb energy and jump to higher energy levels. This process is known as excitation.

4. **Photon Emission**:
- After the electrons are excited to a higher energy level, they do not stay there permanently. They eventually return to their original energy level, releasing the absorbed energy in the form of photons (light).

5. **Oscillation of Electrons**:
- As these free electrons oscillate (move back and forth) between energy levels, they emit light. This oscillation is what contributes to the shiny appearance of metals.

6. **Conclusion**:
- Therefore, the metallic luster is primarily due to the oscillation of loosely bound electrons in response to light, which leads to the emission of photons.

### Final Answer:
Metallic luster is explained by the oscillation of loosely bound electrons in metals, which absorb energy from light and then emit photons when they return to their original energy levels.

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