Among the following chemical reactions the irreversible reaction is

Options

A. `H_(2)+I_(2)rarr2HI`
B. `AgNO_(3)+NaClrarrAgCl+NaNO_(3)`
C. `CaCO_(3)rarr CaO+CO_(2)`
D. `O_(2)+2SO_(2)rarr2SO_(3)`

Answer

To determine which of the given chemical reactions is irreversible, we need to analyze each option based on the nature of the reactions and the formation of products.

### Step-by-Step Solution:

1. **Understanding Irreversible Reactions**:
- Irreversible reactions are those that proceed in one direction only, where the reactants are converted into products and cannot be converted back to the original reactants. A common characteristic of irreversible reactions is the formation of a precipitate or gas that cannot be easily reversed.

2. **Analyzing the Options**:
- **Option 1: H₂ + I₂ → 2HI**
- This reaction involves the combination of hydrogen and iodine gases to form hydrogen iodide. This reaction can be reversed under certain conditions, so it is a reversible reaction.

- **Option 2: AgNO₃ + NaCl → AgCl + NaNO₃**
- In this reaction, silver nitrate reacts with sodium chloride to form silver chloride (AgCl), which is a white precipitate. The formation of this precipitate indicates that the reaction is irreversible because once AgCl is formed, it is difficult to convert it back to the reactants.

- **Option 3: CaCO₃ → CaO + CO₂**
- This reaction involves the decomposition of calcium carbonate into calcium oxide and carbon dioxide. While it may seem irreversible at first, the reverse reaction can occur under the right conditions (combining CaO and CO₂ can regenerate CaCO₃), making this a reversible reaction.

- **Option 4: N₂ + 3H₂ ⇌ 2NH₃**
- This is the synthesis of ammonia from nitrogen and hydrogen gases. This reaction is reversible as it can proceed in both directions under appropriate conditions.

3. **Conclusion**:
- The only irreversible reaction among the options provided is **Option 2: AgNO₃ + NaCl → AgCl + NaNO₃**.

### Final Answer:
The irreversible reaction is **AgNO₃ + NaCl → AgCl + NaNO₃**.

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