The energy of molecules present on the surface of a substance is -

Options

A. Equal to that of molecules is bulk
B. Greater than that of interior molecules
C. Less than that of interior molecules
D. Dependent on nature of substance

Answer

To solve the question regarding the energy of molecules present on the surface of a substance, we can analyze the situation step by step.

### Step-by-Step Solution:

1. **Understanding Molecular Forces**:
- Molecules in a substance experience attractive forces from neighboring molecules. These forces are stronger for molecules that are surrounded by other molecules (bulk) compared to those at the surface.

2. **Comparing Surface and Interior Molecules**:
- A molecule located at the surface of a liquid (like water) is only partially surrounded by other molecules. In contrast, a molecule located in the bulk (interior) is surrounded by other molecules on all sides.

3. **Energy Considerations**:
- The energy of a molecule is related to the strength of the attractive forces acting on it. Molecules at the surface experience weaker attractive forces because they are not fully surrounded. As a result, they have higher potential energy compared to those in the bulk.

4. **Evaluating the Options**:
- Option 1: "Equal to that of molecules in bulk" - This is incorrect because surface molecules have higher energy due to weaker attractive forces.
- Option 2: "Greater than that of interior molecules" - This is correct since surface molecules have higher energy.
- Option 3: "Less than that of interior molecules" - This is incorrect for the same reason as option 1.
- Option 4: "Dependent on the nature of substances" - This is also incorrect because the energy difference is a general property of surface molecules compared to bulk molecules, not dependent on the substance.

5. **Conclusion**:
- The correct answer is that the energy of molecules present on the surface of a substance is **greater than that of interior molecules**.

### Final Answer:
The energy of molecules present on the surface of a substance is **greater than that of interior molecules**.

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