The rate of `S_N2` reaction is maximum when the solvent is

Options

A. methyl alcohol
B. water
C. dimethyl sulphoxide
D. benzene

Explanation

To determine the solvent in which the rate of an \( S_N2 \) reaction is maximum, we can follow these steps:

### Step 1: Understand \( S_N2 \) Reactions
The \( S_N2 \) (substitution nucleophilic bimolecular) reaction involves a nucleophile attacking an electrophile, leading to the substitution of one group for another. The rate of this reaction depends on the nature of the solvent used.

**Hint:** Recall that \( S_N2 \) reactions involve a nucleophile attacking a substrate, and the solvent can influence the rate of this reaction.

### Step 2: Identify the Role of Solvents
Solvents can be broadly classified into two categories: polar protic and polar aprotic.
- **Polar protic solvents** have hydrogen atoms attached to electronegative atoms (like O or N) and can form hydrogen bonds.
- **Polar aprotic solvents** do not have hydrogen atoms attached to electronegative atoms and cannot form hydrogen bonds.

**Hint:** Consider how the ability to form hydrogen bonds affects the nucleophile's reactivity in the solvent.

### Step 3: Analyze the Effect of Solvent Type
In \( S_N2 \) reactions, polar aprotic solvents are preferred because:
- They stabilize the cation formed during the reaction without stabilizing the nucleophile too much.
- They allow the nucleophile to remain reactive, which is crucial for the reaction to proceed efficiently.

**Hint:** Think about how the stabilization of the nucleophile can impact its ability to attack the electrophile.

### Step 4: Evaluate the Given Options
Given the options:
- **A. Methyl alcohol (polar protic)**
- **B. Water (polar protic)**
- **C. Dimethyl sulfoxide (DMSO, polar aprotic)**
- **D. Benzene (non-polar)**

From these options, both methyl alcohol and water are polar protic solvents, which will hinder the \( S_N2 \) reaction due to their hydrogen bonding capabilities. Benzene is non-polar and not suitable for \( S_N2 \) reactions.

**Hint:** Identify which solvent type (protic or aprotic) is most beneficial for the \( S_N2 \) mechanism.

### Step 5: Conclusion
The best solvent for maximizing the rate of an \( S_N2 \) reaction is **C. Dimethyl sulfoxide (DMSO)**, as it is a polar aprotic solvent that enhances nucleophilicity and facilitates the reaction.

**Final Answer:** The rate of \( S_N2 \) reaction is maximum when the solvent is **C. Dimethyl sulfoxide (DMSO)**.