A primary alkyl halide would prefer to undergo :-

Options

A. `S_(N)1` reaction
B. `S_(N)2` reaction
C. `alpha`-elimination
D. racemisation

Explanation

To determine which reaction a primary alkyl halide would prefer to undergo, let's analyze the options step by step.

### Step 1: Understanding Primary Alkyl Halides
A primary alkyl halide is one where the carbon atom bonded to the halogen is attached to only one other carbon atom. For example, methyl bromide (CH3Br) is a primary alkyl halide.

**Hint:** Identify the structure of primary alkyl halides and their characteristics.

### Step 2: Analyzing Reaction Mechanisms
There are two main types of nucleophilic substitution reactions: SN1 and SN2.

- **SN1 Mechanism:** This mechanism involves a two-step process where the alkyl halide first forms a carbocation intermediate. This mechanism is favored by tertiary alkyl halides due to their stability. Primary alkyl halides do not form stable carbocations and thus do not favor SN1 reactions.

- **SN2 Mechanism:** This is a one-step process where the nucleophile attacks the carbon atom at the same time as the leaving group (halogen) departs. This mechanism is favored by primary alkyl halides because there is less steric hindrance, allowing for easier access to the carbon atom.

**Hint:** Compare the characteristics of SN1 and SN2 mechanisms and their suitability for primary alkyl halides.

### Step 3: Evaluating Other Options
- **Alpha Elimination:** This reaction typically involves the removal of two groups (usually a halogen and a hydrogen) from adjacent carbon atoms. It is not favored for primary alkyl halides due to instability.

- **Racemization:** This process involves the formation of a racemic mixture (equal amounts of enantiomers) and is associated with SN1 reactions where a planar carbocation is formed. Since primary alkyl halides do not favor SN1 mechanisms, racemization is not applicable here.

**Hint:** Consider the stability and feasibility of alternative reactions for primary alkyl halides.

### Conclusion
Based on the analysis, a primary alkyl halide would prefer to undergo the **SN2 reaction** due to its structure and the mechanism's suitability for less hindered substrates.

**Final Answer:** A primary alkyl halide would prefer to undergo **SN2 reaction**.