Concept:The acidic strength of hydrogen halides (HX) depends primarily on the bond dissociation energy of the H-X bond. The weaker the bond, the easier it is for the molecule to donate a proton (\( \text{H}^+ \)) in solution.
Solution:- As we move down the halogen group (from F to I), the atomic size of the halogen increases significantly.
- The larger size of Iodine means the H-I bond length is the longest, making it the weakest bond among the hydrogen halides.
- Because it has the least bond energy, HI dissociates most readily in water to yield \( \text{H}^+ \) ions.
- Therefore, the decreasing order of acidic strength is: HI > HBr > HCl > HF.
Why other options are incorrect:- Option A (HF): Although Fluorine is the most electronegative, the H-F bond is extremely short and strong, plus HF forms strong intermolecular hydrogen bonds. This prevents it from fully dissociating, making it a weak acid in water.
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