Which of the following is (are) endothermicn reaction:

Options

A. Combustion of methane
B. Decomposition of water
C. Dehydrogenation of ethane to ethylene
D. Conversion of graphite to diamond

Explanation

To determine which of the given reactions are endothermic, we need to analyze each option based on the energy changes that occur during the reactions. An endothermic reaction is one that absorbs energy (usually in the form of heat) from its surroundings.

### Step-by-Step Solution:

1. **Identify the Reactions**:
- A) Combustion of Methane
- B) Decomposition of Water
- C) Dehydrogenation of Ethane to Ethylene
- D) Conversion of Graphite to Diamond

2. **Analyze Each Reaction**:
- **A) Combustion of Methane**:
- Combustion reactions are characterized by the release of energy. The combustion of methane (CH₄ + 2O₂ → CO₂ + 2H₂O) releases heat and is therefore **exothermic**.
- **Conclusion**: Not an endothermic reaction.

- **B) Decomposition of Water**:
- The decomposition of water (2H₂O → 2H₂ + O₂) requires energy to break the bonds between hydrogen and oxygen atoms. This process absorbs heat from the surroundings, making it an **endothermic** reaction.
- **Conclusion**: This is an endothermic reaction.

- **C) Dehydrogenation of Ethane to Ethylene**:
- The reaction involves breaking C-H bonds in ethane (C₂H₆ → C₂H₄ + H₂), which requires energy input. Thus, this reaction absorbs heat and is classified as **endothermic**.
- **Conclusion**: This is an endothermic reaction.

- **D) Conversion of Graphite to Diamond**:
- The transformation from graphite to diamond involves rearranging carbon atoms into a more ordered structure. Since diamond is less stable than graphite, energy is required to facilitate this conversion, indicating that it is an **endothermic** reaction.
- **Conclusion**: This is an endothermic reaction.

3. **Final Answer**:
- The endothermic reactions among the options are:
- B) Decomposition of Water
- C) Dehydrogenation of Ethane to Ethylene
- D) Conversion of Graphite to Diamond

### Summary:
The endothermic reactions are options B, C, and D.