In elimination reactions, the reactivity of alkyl halides is in decreasing order:
Tertiary > Secondary > Primary
Primary > Secondary > Tertiary
Secondary >Primary > Tertiary
None of These

Options

A. T `gt` S `gt` P
B. P `gt` S `gt` T
C. S `gt` P `gt` T
D. none of these

Answer

To solve the question regarding the reactivity of alkyl halides in elimination reactions, we need to understand the mechanisms involved in these reactions and how the structure of alkyl halides affects their reactivity.

### Step-by-Step Solution:

1. **Understanding Elimination Reactions**:
- Elimination reactions involve the removal of two substituents from a molecule, resulting in the formation of a double bond. The two main types of elimination reactions are E1 and E2.

2. **E1 Mechanism**:
- The E1 mechanism is a two-step process where the rate-determining step involves the formation of a carbocation. The stability of the carbocation is crucial for the reaction to proceed.
- The order of stability for carbocations is: Tertiary > Secondary > Primary. This means that tertiary carbocations are the most stable and will form more readily than secondary or primary carbocations.

3. **E2 Mechanism**:
- The E2 mechanism is a one-step process that involves the simultaneous removal of a leaving group and a hydrogen atom. This mechanism requires a strong base and can occur with primary, secondary, and tertiary alkyl halides.
- However, the reactivity order still follows the stability of the alkyl halide, which is influenced by steric hindrance.

4. **Reactivity Order**:
- For elimination reactions, the reactivity of alkyl halides is determined by the stability of the intermediates (carbocations for E1 and transition states for E2).
- Therefore, the general order of reactivity in elimination reactions is:
- Tertiary > Secondary > Primary

5. **Conclusion**:
- Based on the above analysis, the correct answer to the question is that the reactivity of alkyl halides in elimination reactions is in decreasing order: **Tertiary > Secondary > Primary**.

### Final Answer:
The correct option is: **Tertiary > Secondary > Primary**.

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