The interface between a solid and gas may be
represented by
`{:("(a) Solid - gas"," (b) Solid + gas"),("(c) Solid / gas",""):}`

Options

A. a' and 'b'
B. b' and 'c'
C. a' and 'c'
D. Only 'b'

Answer

To solve the question regarding the representation of the interface between a solid and gas, let's break it down step by step:

### Step 1: Understand the Question
The question asks how the interface between a solid and a gas can be represented. We have three representations to consider:
- (a) Solid - gas
- (b) Solid + gas
- (c) Solid / gas

### Step 2: Analyze Each Representation
1. **Solid - gas**: This representation indicates a direct interaction or interface between the solid and the gas. It suggests a boundary where the solid and gas meet, which is a valid representation of the interface.

2. **Solid + gas**: This representation implies an additive relationship rather than an interface. It suggests that the solid and gas coexist without indicating any interaction or boundary, which is not accurate for an interface.

3. **Solid / gas**: This representation also indicates an interface, similar to the first one. The slash suggests a division that highlights the interaction between the solid and gas, making it a valid representation.

### Step 3: Determine the Correct Representations
From the analysis:
- Valid representations of the interface are (a) Solid - gas and (c) Solid / gas.
- The representation (b) Solid + gas is not valid as it does not represent an interface.

### Step 4: Choose the Correct Option
Now, we need to select the correct option based on the valid representations:
- The correct representations are (a) and (c), which means the answer corresponds to the option that includes both A and C.

### Conclusion
The correct answer is option (C): A and C.

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