In Which of the following reaction an acid-base reaction takes place ?

Options

A.
B.
C.
D. All of these

Explanation

To determine which of the reactions involves an acid-base reaction, we can analyze each reaction step by step.

### Step-by-Step Solution:

1. **Understanding Grignard Reagents**:
- Grignard reagents have the general formula R-MgX, where R is an alkyl or aryl group, and X is a halogen.
- They act as strong bases because they contain a carbon atom with a negative charge (R⁻), which can accept protons (H⁺).

2. **Identifying Acid-Base Reactions**:
- An acid-base reaction occurs when a proton (H⁺) is transferred from an acid to a base.
- In this context, R⁻ (from Grignard reagents) acts as a base, and any proton donor (like H⁺ from water or acids) acts as an acid.

3. **Analyzing Each Reaction**:
- **Reaction A**:
- Cyclohexane with CH₂MgCl reacts with water.
- CH₂⁻ (from CH₂MgCl) acts as a base and captures a proton (H⁺) from water, which is an acid.
- This is an acid-base reaction.

- **Reaction B**:
- An organolithium reagent (RLi) reacts with HBr in the presence of water.
- R⁻ (from RLi) can accept H⁺ from HBr or water, making it a base, while HBr acts as an acid.
- This is also an acid-base reaction.

- **Reaction C**:
- Another Grignard reagent reacts with a deuterated compound (D₂O).
- The carbon anion (C⁻) can capture a proton (D⁺) from D₂O, acting as a base, while D₂O acts as an acid.
- This is again an acid-base reaction.

4. **Conclusion**:
- All the reactions analyzed involve the transfer of protons, confirming that they are acid-base reactions.
- Therefore, the answer to the question is that **all of these reactions are acid-base reactions**.

### Final Answer:
**All of these reactions are acid-base reactions.**