Assertion (A) : Formation of HI is a bimolecular reaction.
Reason (R ): Two molecules of reactants are involved in this reaction.

Options

A. If both `(A)` and `(R )` are correct, and `(R )` is the correct explnation of `(A)`.
B. If both `(A)` and `(R )` are correct, but `(R )` is noth the correct explanation of `(A)`.
C. If `(A)` is correct, but `(R )` is incorrect.
D. If `(A)` is incorrect, but `(R )` is correct.

Answer

To solve the assertion-reason question regarding the formation of HI, we can break down the information as follows:

### Step-by-Step Solution:

1. **Understanding the Reaction**:
- The formation of hydrogen iodide (HI) occurs through the reaction of hydrogen gas (H₂) and iodine gas (I₂).
- The balanced chemical equation for this reaction is:
\[ H_2(g) + I_2(g) \rightarrow 2 HI(g) \]

2. **Identifying the Type of Reaction**:
- A bimolecular reaction is defined as a reaction that involves the collision of two reactant molecules.
- In this case, we have two different reactants: H₂ and I₂.

3. **Analyzing the Molecules Involved**:
- Since the reaction involves one molecule of H₂ and one molecule of I₂, we can conclude that two molecules are indeed involved in the reaction.
- Therefore, the formation of HI is classified as a bimolecular reaction.

4. **Rate of Reaction**:
- The rate of this reaction depends on the concentrations of both reactants, H₂ and I₂.
- The rate law for this reaction can be expressed as:
\[ \text{Rate} = k [H_2]^1 [I_2]^1 \]
- Here, the order of the reaction is the sum of the powers of the concentration terms, which is \(1 + 1 = 2\).

5. **Conclusion**:
- Since both the assertion (A) and the reason (R) are correct, and the reason correctly explains the assertion, we conclude that the correct answer is that both the assertion and reason are true.

### Final Answer:
- **Assertion (A)**: True
- **Reason (R)**: True
- Therefore, both the assertion and reason are correct, and the reason correctly explains the assertion.