Which of the following hydrogen halides react with `AgNO_3` to give a precipitate that dissolves in hypo solution ?
(I)HCl (II)HF (III)HI (IV)HBr

Options

A. (III),(I),(II)
B. (I),(III),(IV)
C. (IV),(II),(I)
D. (II),(IV),(III)

Answer

To solve the question, we need to analyze the reactions of the given hydrogen halides with silver nitrate (AgNO3) and determine which of them forms a precipitate that dissolves in hypo solution (sodium thiosulfate, Na2S2O3).

### Step-by-Step Solution:

1. **Identify the Hydrogen Halides**: The given hydrogen halides are:
- (I) HCl (Hydrochloric acid)
- (II) HF (Hydrofluoric acid)
- (III) HI (Hydriodic acid)
- (IV) HBr (Hydrobromic acid)

2. **Reactions with Silver Nitrate**:
- When hydrogen halides react with AgNO3, they form silver halides (AgX) as precipitates.
- The reactions are as follows:
- HCl + AgNO3 → AgCl (white precipitate)
- HF + AgNO3 → No precipitate (HF forms soluble complex)
- HI + AgNO3 → AgI (yellow precipitate)
- HBr + AgNO3 → AgBr (pale yellow precipitate)

3. **Solubility of Precipitates in Hypo Solution**:
- The precipitates formed from HCl, HI, and HBr (AgCl, AgI, and AgBr respectively) can dissolve in hypo solution (Na2S2O3).
- The reaction of the precipitates with hypo solution leads to the formation of soluble complexes:
- AgCl + Na2S2O3 → [Ag(S2O3)2]3- + NaCl
- AgI + Na2S2O3 → [Ag(S2O3)2]3- + NaI
- AgBr + Na2S2O3 → [Ag(S2O3)2]3- + NaBr

4. **Conclusion**:
- HCl does not form a precipitate with AgNO3, while HF does not react to form a precipitate at all.
- Therefore, the hydrogen halides that react with AgNO3 to give a precipitate that dissolves in hypo solution are:
- HI (Hydriodic acid)
- HBr (Hydrobromic acid)
- HCl (Hydrochloric acid)

Thus, the answer is (I) HCl, (III) HI, and (IV) HBr.

### Final Answer:
- The hydrogen halides that react with AgNO3 to give a precipitate that dissolves in hypo solution are: **HCl, HI, and HBr**.