A solid acts as an adsorbent because it has

Options

A. A definite shape
B. Small pores in it
C. Unsaturated valencies
D. A high lattice energy

Explanation

To answer the question "A solid acts as an adsorbent because it has," we need to analyze the properties of solids that enable them to function effectively as adsorbents.

### Step-by-Step Solution:

1. **Definition of Adsorbent**:
- An adsorbent is a material that has the ability to attract and hold molecules of another substance (adsorbate) on its surface. This process is known as adsorption.

2. **Characteristics of Solids**:
- Solids have a definite shape and volume, and they possess a structured arrangement of particles. However, the key feature that allows them to act as adsorbents is related to their surface properties.

3. **Unbalanced Forces of Attraction**:
- In solids, particularly at their surfaces, there exist unbalanced forces of attraction. These forces arise due to the presence of free valencies or unsaturated bonds that are not fully satisfied with neighboring atoms.

4. **Role of Free Valencies**:
- The unbalanced forces or free valencies on the surface of solids create sites that can attract and hold onto molecules of the adsorbate. This is because these sites can interact with the molecules through various forces, such as van der Waals forces, hydrogen bonding, or ionic interactions.

5. **Conclusion**:
- Therefore, the primary reason a solid acts as an adsorbent is due to the presence of unbalanced forces of attraction or free valencies on its surface, which allow it to attract and retain the molecules of the adsorbate.

### Final Answer:
A solid acts as an adsorbent because it has unbalanced forces of attraction or free valencies on its surface.

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