Which of the following reactions are exothermic in nature ?
(i) Evaporation of water
(ii) Dissolution of sodium hydroxide in water
(iii) Dilution of sulphuric acid
(iv) Dissolution of ammonium chloride in water
(v) Combustion of methane gas

Options

A. `(i), (iv)` and `(v)` only
B. `(ii), (iii)` and `(v)` only
C. `(i), (ii)` and `(iv)` only
D. `(i), (iii)` and `(iv)` only

Explanation

To determine which of the given reactions are exothermic in nature, we will analyze each reaction one by one.

### Step 1: Analyze the Evaporation of Water
- **Reaction**: Evaporation of water (H₂O(l) → H₂O(g))
- **Nature**: This process requires energy to convert liquid water into vapor, which means it absorbs heat from the surroundings.
- **Conclusion**: **Endothermic**

### Step 2: Analyze the Dissolution of Sodium Hydroxide in Water
- **Reaction**: Dissolution of sodium hydroxide (NaOH(s) → Na⁺(aq) + OH⁻(aq))
- **Nature**: The dissolution of sodium hydroxide in water releases heat, causing an increase in temperature of the solution.
- **Conclusion**: **Exothermic**

### Step 3: Analyze the Dilution of Sulfuric Acid
- **Reaction**: Dilution of sulfuric acid (H₂SO₄ + H₂O)
- **Nature**: When sulfuric acid is diluted, it releases a significant amount of heat. This is due to the strong exothermic nature of the reaction when concentrated acid is mixed with water.
- **Conclusion**: **Exothermic**

### Step 4: Analyze the Dissolution of Ammonium Chloride in Water
- **Reaction**: Dissolution of ammonium chloride (NH₄Cl(s) → NH₄⁺(aq) + Cl⁻(aq))
- **Nature**: The dissolution of ammonium chloride in water absorbs heat, resulting in a decrease in temperature of the solution.
- **Conclusion**: **Endothermic**

### Step 5: Analyze the Combustion of Methane Gas
- **Reaction**: Combustion of methane (CH₄ + 2O₂ → CO₂ + 2H₂O)
- **Nature**: The combustion of methane releases a large amount of heat and light, making it an exothermic reaction.
- **Conclusion**: **Exothermic**

### Final Summary
Based on the analysis:
- **Exothermic Reactions**:
1. Dissolution of sodium hydroxide in water
2. Dilution of sulfuric acid
3. Combustion of methane gas

- **Endothermic Reactions**:
1. Evaporation of water
2. Dissolution of ammonium chloride in water