Assertion (A) : In the reaction, `N_(2)+3H_(2) rarr 2NH_(3)`, the rate of reaction is different in terms of `N_(2), H_(2)` and `NH_(3)`.
Reason (R ): The rate of reaction is equal to the rate of disappearance of a reactant or rate of formation of a Product.

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 both (A) and (R ) are incorrect.

Explanation

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

### Step 1: Understand the Reaction
The given reaction is:
\[ N_2 + 3H_2 \rightarrow 2NH_3 \]

### Step 2: Write the Rate Expressions
The rate of a reaction can be expressed in terms of the change in concentration of the reactants and products over time.

1. For nitrogen (\(N_2\)):
\[ \text{Rate} = -\frac{d[N_2]}{dt} \]

2. For hydrogen (\(H_2\)):
\[ \text{Rate} = -\frac{1}{3} \frac{d[H_2]}{dt} \]
(Here, we divide by 3 because 3 moles of \(H_2\) are consumed for every mole of \(N_2\) that reacts.)

3. For ammonia (\(NH_3\)):
\[ \text{Rate} = \frac{1}{2} \frac{d[NH_3]}{dt} \]
(Here, we divide by 2 because 2 moles of \(NH_3\) are produced for every mole of \(N_2\) that reacts.)

### Step 3: Compare the Rates
From the expressions above, we can see that the rates are related by their stoichiometric coefficients:
- The rate of disappearance of \(N_2\) is equal to the rate of disappearance of \(H_2\) divided by 3.
- The rate of formation of \(NH_3\) is equal to the rate of disappearance of \(N_2\) multiplied by 2.

Thus, while the rates are related, they are not numerically the same due to the stoichiometric coefficients.

### Step 4: Analyze the Assertion and Reason
- **Assertion (A)** states that the rate of reaction is different in terms of \(N_2\), \(H_2\), and \(NH_3\). This is **true** because the rates are expressed differently based on their stoichiometric coefficients.

- **Reason (R)** states that the rate of reaction is equal to the rate of disappearance of a reactant or the rate of formation of a product. This is also **true**, but it does not justify the assertion correctly because it does not account for the stoichiometric coefficients.

### Conclusion
Both the assertion and the reason are true, but the assertion is misleading without considering the stoichiometric coefficients. Therefore, the correct answer is that the assertion is true, and the reason is true but does not explain the assertion.

### Final Answer
- Assertion (A) is true.
- Reason (R) is true but does not explain (A).