Which of the following is a double displacement reaction?

Options

A. `NH_3 + HCl to NH_4Cl`
B. `CuSO_4 +Fe to FeSO_4 +Cu`
C. `Na_2SO_4 + BaCl_2 to BaSO_4 + 2NaCl`
D. `CaCO_3 to CaO+CO_2`

Explanation

To identify which of the given reactions is a double displacement reaction, we can follow these steps:

### Step 1: Understand the Definition of Double Displacement Reaction
A double displacement reaction occurs when two compounds exchange ions to form two new compounds. The general form of a double displacement reaction can be represented as:
\[ AB + CD \rightarrow AC + BD \]
Here, A and C are cations, while B and D are anions.

### Step 2: Analyze Each Option
Let's analyze each option provided to determine if it fits the criteria for a double displacement reaction.

#### Option A: Ammonia + HCl → NH4Cl
- This reaction is a combination reaction where two reactants combine to form a single product.
- **Conclusion**: Not a double displacement reaction.

#### Option B: CuSO4 + Fe → FeSO4 + Cu
- In this reaction, iron (Fe) displaces copper (Cu) from copper sulfate (CuSO4). This is a single displacement reaction.
- **Conclusion**: Not a double displacement reaction.

#### Option C: Na2SO4 + BaCl2 → BaSO4 + 2NaCl
- Here, sodium (Na) and barium (Ba) are exchanging their anions (sulfate and chloride). This fits the definition of a double displacement reaction.
- **Conclusion**: This is a double displacement reaction.

#### Option D: CaCO3 → CaO + CO2
- This reaction involves the breakdown of calcium carbonate into calcium oxide and carbon dioxide. It is a decomposition reaction.
- **Conclusion**: Not a double displacement reaction.

### Step 3: Final Identification
After analyzing all the options, we find that:
- The only reaction that qualifies as a double displacement reaction is **Option C: Na2SO4 + BaCl2 → BaSO4 + 2NaCl**.

### Final Answer
The double displacement reaction is **Option C: Na2SO4 + BaCl2 → BaSO4 + 2NaCl**.

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