Assertion `(A)`: `MeMgBr` should be preapared under perfectly anhydrous conditions.
Reason `(R): Grinard reagent reacts with water.

Options

A. Both `(A)` and `(R)` are true and `(R0` is the correct explanation of `(A)`.
B. Both `(A)` and `(R)` are true but `(R)` is not the correct explanation of `(A)`.
C. `(A) is true but `(R)` is false.
D. `(A) is false but `(R)` is true.

Explanation

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 `MeMgBr` (methylmagnesium bromide) should be prepared under perfectly anhydrous conditions.
- This means that the preparation must occur in the absence of water.

2. **Understanding the Reason (R)**:
- The reason states that Grignard reagents react with water.
- When a Grignard reagent comes into contact with water, it reacts to produce an alkane and a hydroxide compound.

3. **Reaction of Grignard Reagents with Water**:
- The general reaction can be represented as:
\[ R-MgX + H_2O \rightarrow R-H + Mg(OH)X \]
- For `MeMgBr`, the reaction with water would yield methane (CH₄) and magnesium hydroxide bromide (Mg(OH)Br).

4. **Conclusion**:
- Since Grignard reagents are highly reactive and will react with water to form unwanted products, it is crucial to prepare them under anhydrous conditions to ensure their stability and reactivity for subsequent reactions.
- Therefore, both the assertion and the reason are correct, and the reason provided is a correct explanation of the assertion.

### Final Answer:
Both assertion (A) and reason (R) are correct, and the reason is the correct explanation of the assertion.