Which of the following is a decomposition reaction?

Options

A. `ZnCO_(3)toZnO+CO_(2)`
B. `BaCl_(2)+Na_(2)SO_(4)toBaSO_(4)+2NaCl`
C. `Zn+2HCl toZnCl_(2)+H_(2)`
D. `3MnO_(2)+4Al to3Mn+2Al_(2)O_(3)`

Explanation

To determine which of the given reactions is a decomposition reaction, we need to understand what a decomposition reaction is. A decomposition reaction occurs when a single reactant breaks down into two or more products.

Let's analyze each option step by step:

### Step 1: Understand Decomposition Reaction
- A decomposition reaction involves one reactant that breaks down into two or more products.

### Step 2: Analyze Option A
- **Reaction:** ZnCO3 → ZnO + CO2
- Here, we have one reactant (ZnCO3) that decomposes into two products (ZnO and CO2).
- **Conclusion:** This is a decomposition reaction.

### Step 3: Analyze Option B
- **Reaction:** BaCl2 + Na2SO4 → BaSO4 + 2 NaCl
- This reaction involves two reactants (BaCl2 and Na2SO4) reacting to form two products (BaSO4 and NaCl).
- **Conclusion:** This is a double displacement reaction, not a decomposition reaction.

### Step 4: Analyze Option C
- **Reaction:** Zn + 2 HCl → ZnCl2 + H2
- In this reaction, zinc (Zn) reacts with hydrochloric acid (HCl) to produce zinc chloride (ZnCl2) and hydrogen (H2).
- **Conclusion:** This is a single displacement reaction, not a decomposition reaction.

### Step 5: Analyze Option D
- **Reaction:** 3MnO2 + 4Al → 3Mn + 2Al2O3
- This reaction involves manganese dioxide (MnO2) and aluminum (Al) reacting to form manganese (Mn) and aluminum oxide (Al2O3).
- **Conclusion:** This is a redox reaction, not a decomposition reaction.

### Final Conclusion
After analyzing all the options, we find that:
- **Option A (ZnCO3 → ZnO + CO2)** is the only decomposition reaction.

### Summary of the Solution
The correct answer is **Option A: ZnCO3 → ZnO + CO2**, as it is the only reaction where a single reactant decomposes into two products.

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