(A) The formation of `SO_(3)` by contact process is an example of heterogeneous catalysis
(R): The reactants and product are in different phase in the formation of `SO_(3)` by contact process 

Options

A. Both A & R are true, R is the correct explanation of A
B. Both A & R are true, R is not correct explanation of A
C. A is true, R is false
D. A is false, R is true

Answer

To solve the question, we need to analyze both the assertion (A) and the reason (R) provided:

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that the formation of SO₃ by the contact process is an example of heterogeneous catalysis.
- In the contact process, sulfur dioxide (SO₂) reacts with oxygen (O₂) to form sulfur trioxide (SO₃). This reaction can be represented as:
\[ 2 \text{SO}_2(g) + \text{O}_2(g) \rightarrow 2 \text{SO}_3(g) \]

2. **Identifying the Catalyst**:
- The catalyst used in the contact process is vanadium pentoxide (V₂O₅), which is in solid form.

3. **Determining the Phases of Reactants and Products**:
- In the reaction:
- SO₂ is in the gaseous state.
- O₂ is in the gaseous state.
- SO₃ is also in the gaseous state.
- V₂O₅ (the catalyst) is in the solid state.
- Here, we can see that the reactants (SO₂ and O₂) and the product (SO₃) are all in the gaseous state, while the catalyst (V₂O₅) is in a different phase (solid).

4. **Understanding Heterogeneous Catalysis**:
- Heterogeneous catalysis occurs when the catalyst is in a different phase than the reactants and products. In this case, since the catalyst is solid and the reactants/products are gases, the assertion (A) is true.

5. **Understanding the Reason (R)**:
- The reason states that the reactants and products are in different phases in the formation of SO₃ by the contact process.
- However, while the catalyst is in a different phase, the reactants (SO₂ and O₂) and the product (SO₃) are all in the same phase (gaseous). Therefore, the reason (R) is false.

6. **Conclusion**:
- Since the assertion (A) is true and the reason (R) is false, the correct answer is:
- A is true, R is false.

### Final Answer:
- A is true, R is false.