Arrange the followingg hydrogen halides in order of their decreasin reactivity with propene.

Options

A. HCl>HBr>HI
B. HBr>HI>HCl
C. HI>HBr>HCl
D. HCl>HI>HBr

Explanation

To arrange the hydrogen halides (HCl, HBr, HI, and HF) in order of their decreasing reactivity with propene, we will analyze the factors that influence their reactivity in nucleophilic addition reactions.

### Step-by-Step Solution:

1. **Identify the Reaction Type**:
- The reaction between propene (C3H6) and hydrogen halides is a nucleophilic addition reaction. The hydrogen halide adds across the double bond of propene.

2. **Understand Markovnikov's Rule**:
- According to Markovnikov's rule, the hydrogen atom from the hydrogen halide will attach to the carbon with more hydrogen atoms, while the halide ion will attach to the carbon with fewer hydrogen atoms. This leads to the formation of a more stable carbocation intermediate.

3. **Evaluate the Strength of Hydrogen Halides**:
- The reactivity of hydrogen halides is influenced by the strength of the H-X bond. We need to consider the bond lengths and bond strengths of HCl, HBr, HI, and HF:
- HF has a very strong bond due to the small size of fluorine, making it less reactive.
- HCl has a shorter bond length and is less reactive than HBr and HI.
- HBr has a longer bond length than HCl but shorter than HI, making it more reactive than HCl.
- HI has the longest bond length and weakest bond strength, making it the most reactive.

4. **Rank the Hydrogen Halides**:
- Based on the bond strengths and lengths, we can rank the hydrogen halides in order of their decreasing reactivity with propene:
- HI > HBr > HCl > HF

5. **Conclusion**:
- The order of decreasing reactivity of hydrogen halides with propene is: **HI > HBr > HCl > HF**.

### Final Answer:
The correct order of decreasing reactivity with propene is: **HI > HBr > HCl > HF**.