The electric bulb on long use forms a black coating on its inner surface. The process associated with this is

Options

A. melting of tungsten `
B. sublimation of tungsten
C. oxidation of tungsten
D. reduction of tungsten

Explanation

**Step-by-Step Solution:**

1. **Understanding the Problem**: When an electric bulb is used for a long time, it develops a black coating on its inner surface. This phenomenon needs to be explained.

2. **Identifying the Cause**: The black coating is primarily due to the evaporation of the filament material, which is usually tungsten. When the filament heats up, it sublimates, meaning it transitions from a solid state directly to a gas without becoming liquid.

3. **Sublimation Process**: As the tungsten filament sublimates, the gas produced can deposit on the cooler inner surface of the bulb. Over time, this results in a black coating forming on the glass.

4. **Conclusion**: The process associated with the formation of the black coating on the inner surface of the electric bulb is sublimation of the filament material (tungsten).

**Final Answer**: The process associated with the black coating on the inner surface of an electric bulb after long use is sublimation.

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