Give an example of a reaction which is combination as well as exothermic.

Explanation

To solve the question, we need to provide an example of a reaction that is both a combination reaction and an exothermic reaction. Let's break it down step by step:

### Step 1: Define Combination Reaction
A combination reaction is a type of chemical reaction where two or more reactants combine to form a single product.

**Hint:** Look for a reaction where multiple reactants come together to create one new substance.

### Step 2: Define Exothermic Reaction
An exothermic reaction is a reaction that releases heat energy to the surroundings.

**Hint:** Consider reactions that produce heat, often felt as an increase in temperature during the reaction.

### Step 3: Identify an Example
One classic example of a reaction that is both a combination and exothermic is the reaction between calcium oxide (CaO) and water (H₂O).

**Hint:** Think of common substances that react with water to form a new compound while releasing heat.

### Step 4: Write the Reaction
The reaction can be represented as follows:
\[ \text{CaO (s)} + \text{H}_2\text{O (l)} \rightarrow \text{Ca(OH)}_2 (aq) \]
This reaction forms calcium hydroxide (Ca(OH)₂), also known as slaked lime.

**Hint:** Ensure that the products are a single compound formed from the reactants.

### Step 5: Describe the Heat Release
During the reaction, heat is released, which can be observed as the temperature of the mixture increases. This indicates that the reaction is exothermic.

**Hint:** Remember to mention the observable effect of heat release in the context of the reaction.

### Final Answer
Thus, the reaction between calcium oxide and water is an example of a reaction that is both a combination reaction and exothermic:
\[ \text{CaO (s)} + \text{H}_2\text{O (l)} \rightarrow \text{Ca(OH)}_2 (aq) \]
This reaction releases heat, making it exothermic.