In `S_N2` reactions, the correct order of reactivity for the following compounds:
`CH_3Cl,CH_3CH_2Cl,(CH_3)_2CHCl "and" (CH_3)_3"CC"l` is :

Options

A. `CH_3Cl gt (CH_3)_2CHCl gt CH_3CH_2Cl gt (CH_3)_3CCl`
B. `CH_3Cl gt CH_3CH_2Cl gt (CH_3)_2CHCl gt (CH_3)_3CCl`
C. `CH_3CH_2Cl gt CH_3Cl gt (CH_3)_2CHCl gt (CH_3)_3CCl`
D. `(CH_3)_2CHCl gt CH_3CH_2Cl gt CH_3Cl gt (CH_3)_3CCl`

Explanation

To determine the correct order of reactivity for the compounds in \( S_N2 \) reactions, we need to consider the steric hindrance around the carbon atom that is bonded to the halogen (in this case, chlorine). The more sterically hindered the carbon is, the slower the reaction will be due to the nucleophile's inability to effectively attack the carbon atom.

### Step-by-Step Solution:

1. **Identify the Compounds**: The compounds given are:
- \( CH_3Cl \) (methyl chloride)
- \( CH_3CH_2Cl \) (ethyl chloride)
- \( (CH_3)_2CHCl \) (isopropyl chloride)
- \( (CH_3)_3CCl \) (tert-butyl chloride)

2. **Analyze Steric Hindrance**:
- **Methyl Chloride (\( CH_3Cl \))**: This compound has no alkyl groups attached to the carbon bonded to chlorine, making it the least hindered and therefore the most reactive in \( S_N2 \) reactions.
- **Ethyl Chloride (\( CH_3CH_2Cl \))**: This compound has one alkyl group, which introduces some steric hindrance but is still less hindered than the next compounds.
- **Isopropyl Chloride (\( (CH_3)_2CHCl \))**: This compound has two alkyl groups attached, increasing the steric hindrance and making it less reactive than methyl and ethyl chlorides.
- **Tert-butyl Chloride (\( (CH_3)_3CCl \))**: This compound has three alkyl groups, resulting in significant steric hindrance, making it the least reactive in \( S_N2 \) reactions.

3. **Order of Reactivity**: Based on the analysis of steric hindrance, the order of reactivity for these compounds in \( S_N2 \) reactions is:
\[ CH_3Cl > CH_3CH_2Cl > (CH_3)_2CHCl > (CH_3)_3CCl \]

### Final Answer:
The correct order of reactivity for the given compounds in \( S_N2 \) reactions is:
\[ CH_3Cl > CH_3CH_2Cl > (CH_3)_2CHCl > (CH_3)_3CCl \]