The chemical reaction between Calcium oxide and water is:

Options

A. Endothermic reaction
B. Decomposition reaction
C. Exothermic reaction
D. Displacement reaction

Explanation

To determine the nature of the chemical reaction between calcium oxide (CaO) and water (H2O), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Reactants**: The reactants in this reaction are calcium oxide (CaO) and water (H2O).

2. **Write the Reaction**: When calcium oxide reacts with water, the chemical equation can be written as:
\[ \text{CaO} + \text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 \]
This product is known as slaked lime or calcium hydroxide.

3. **Determine the Type of Reaction**:
- **Exothermic vs. Endothermic**: An exothermic reaction releases heat, while an endothermic reaction absorbs heat. In this case, when CaO reacts with H2O, it releases heat.
- **Decomposition Reaction**: This type of reaction involves a single compound breaking down into two or more products. Since CaO and H2O are combining to form a single product (Ca(OH)2), this is not a decomposition reaction.
- **Displacement Reaction**: This occurs when one element displaces another in a compound. In this reaction, no element is displacing another, so it is not a displacement reaction.

4. **Conclusion**: Since the reaction releases heat, it is classified as an exothermic reaction. Therefore, the correct answer is that the reaction between calcium oxide and water is an exothermic reaction.

### Final Answer:
The chemical reaction between calcium oxide and water is an **exothermic reaction**.

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