In heterogeneous catalytic reactions, catalyst in the finely divided form possesses higher catalytic reactivity. This is because 

Options

A. surface area of the finely divided catalyst is large
B. surface area of the catalyst in the lump form is large
C. finely divided catalyst has more internal energy in it
D. finely divided catalyst has stable surface

Answer

To solve the question regarding why finely divided catalysts possess higher catalytic reactivity in heterogeneous catalytic reactions, we can break down the reasoning into clear steps:

### Step-by-Step Solution:

1. **Understanding Heterogeneous Catalysis**:
- Heterogeneous catalysis involves reactions where the reactants and the catalyst are in different phases. For example, gases reacting with a solid catalyst.

2. **Role of Surface Area**:
- The effectiveness of a catalyst is significantly influenced by its surface area. A larger surface area allows for more reactant molecules to interact with the catalyst.

3. **Finely Divided Catalyst**:
- A finely divided catalyst has a much larger surface area compared to a lump or bulk catalyst. This is because breaking down the catalyst into smaller particles increases the total surface area available for reactions.

4. **Adsorption of Reactants**:
- In heterogeneous catalysis, reactants must adsorb onto the surface of the catalyst to participate in the reaction. A finely divided catalyst can adsorb more reactant molecules due to its larger surface area.

5. **Increased Reaction Rate**:
- With more reactant molecules adsorbed on the surface of the finely divided catalyst, the likelihood of collisions and subsequent reactions increases, leading to a higher reaction rate.

6. **Conclusion**:
- Therefore, the primary reason that finely divided catalysts possess higher catalytic reactivity is that they provide a larger surface area for the adsorption of reactants, facilitating more effective reactions.

### Final Answer:
In heterogeneous catalytic reactions, catalysts in the finely divided form possess higher catalytic reactivity because the surface area of the finely divided catalyst is large.