Assertion (A) : For: `aA+bB rarr` Product. The order of reaction is equal to `(a+b)`.
Reason (R ): Rate of reaction `=k[A]^(a)[B]^(b)`.

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 regarding the assertion and reason provided, we will break it down step by step.

### Step 1: Understand the Assertion
The assertion states that for the reaction \( aA + bB \rightarrow \text{Products} \), the order of the reaction is equal to \( (a + b) \).

### Step 2: Understand the Reason
The reason given is that the rate of reaction is expressed as:
\[ \text{Rate} = k[A]^a[B]^b \]
where \( k \) is the rate constant, \( [A] \) is the concentration of reactant A raised to the power \( a \), and \( [B] \) is the concentration of reactant B raised to the power \( b \).

### Step 3: Define Reaction Order
The order of a reaction is defined as the sum of the powers of the concentration terms in the rate law. In this case, the rate law is given as \( k[A]^a[B]^b \).

### Step 4: Calculate the Order of Reaction
From the rate law:
- The power of \( [A] \) is \( a \).
- The power of \( [B] \) is \( b \).

Thus, the order of the reaction can be calculated as:
\[ \text{Order} = a + b \]

### Step 5: Conclusion
Since both the assertion and the reason are correct, and the reason correctly explains the assertion, we conclude that:
- Both the assertion (A) and reason (R) are correct.
- The reason (R) is the correct explanation of the assertion (A).

### Final Answer
Both the assertion and reason are correct, and the reason is the correct explanation of the assertion.

---