Assertion (A) : The molecularity of the reaction
`H_(2) + Br_(2) rarr 2HBr` is `2`.
Reason (R ): The order of the reaction is `3//2`.

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.

Explanation

To solve the question, we need to analyze both the assertion and the reason provided.

### Step-by-Step Solution:

1. **Understanding Molecularity**:
- Molecularity refers to the number of reactant molecules that collide in an elementary reaction step.
- For the reaction \( H_2 + Br_2 \rightarrow 2HBr \), there are two reactants: one molecule of \( H_2 \) and one molecule of \( Br_2 \).
- Therefore, the molecularity of this reaction is \( 1 + 1 = 2 \).

2. **Understanding Order of Reaction**:
- The order of a reaction is the sum of the powers to which the concentration terms are raised in the rate law expression.
- The rate law for the reaction can be expressed as:
\[ \text{Rate} = k [H_2]^x [Br_2]^y \]
- The order of the reaction is given as \( x + y \).

3. **Evaluating the Reason**:
- The reason states that the order of the reaction is \( \frac{3}{2} \) (or \( 1.5 \)).
- This implies that \( x + y = \frac{3}{2} \).
- However, the order of a reaction must be determined experimentally and cannot be deduced solely from the stoichiometry of the balanced equation.

4. **Conclusion**:
- The assertion (A) is correct: the molecularity of the reaction is indeed 2.
- The reason (R) is also correct: the order of the reaction can be stated as \( \frac{3}{2} \), but it does not explain the assertion.
- Therefore, the correct answer is that both A and R are correct, but R is not the correct explanation of A.

### Final Answer:
- Assertion (A) is true.
- Reason (R) is true but does not explain A.
- Hence, the answer is: Both A and R are correct, but R is not the correct explanation of A.