Which of the following interface cannot be obtained?

Options

A. Liquid=liquid
B. Solid-liquid
C. Liquid-gas
D. Gas-gas

Explanation

To solve the question of which interface cannot be obtained, we will analyze each of the provided options step by step.

### Step 1: Analyze Liquid-Liquid Interface
- **Example**: Consider mixing oil and water. When you mix them, oil floats on top of water, creating two distinct layers.
- **Conclusion**: A liquid-liquid interface can be obtained.

### Step 2: Analyze Solid-Liquid Interface
- **Example**: When NaCl crystals are placed in a NaCl solution, the solid NaCl can dissolve into the liquid, and the dissolved NaCl can crystallize out.
- **Conclusion**: A solid-liquid interface can be obtained.

### Step 3: Analyze Liquid-Gas Interface
- **Example**: When water is boiled, water molecules transition from the liquid phase to the gas phase, creating a surface where the liquid and gas meet.
- **Conclusion**: A liquid-gas interface can be obtained.

### Step 4: Analyze Gas-Gas Interface
- **Explanation**: Gases are completely miscible, meaning they mix thoroughly without forming distinct layers. For example, if you take a mixture of oxygen and nitrogen, you cannot define a boundary between the two gases.
- **Conclusion**: A gas-gas interface cannot be obtained.

### Final Answer
The interface that cannot be obtained is **gas-gas**.

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