Identify endothermic reaction among the following:

Options

A. passage of `CO_2` through red hot carbon
B. passage of `O_2` through red hot carbon
C. burning of methane
D. burning of water gas

Answer

To identify the endothermic reaction among the given options, we need to understand the definitions of endothermic and exothermic reactions.

### Step-by-Step Solution:

1. **Understand the Definitions**:
- **Endothermic Reaction**: A reaction that absorbs heat from its surroundings. This means that energy is required for the reaction to occur.
- **Exothermic Reaction**: A reaction that releases heat to its surroundings. This means that energy is produced during the reaction.

2. **Analyze the Options**:
- We have four reactions to consider. We need to determine whether each reaction is endothermic or exothermic.

3. **Evaluate Each Option**:
- **Option 1: Burning of water gas** (a mixture of hydrogen and carbon monoxide):
- This reaction releases heat. Therefore, it is an **exothermic reaction**.
- **Option 2: Burning of methane**:
- This is a combustion reaction that also releases heat. Thus, it is an **exothermic reaction**.
- **Option 3: Passage of O2 through red hot carbon**:
- This reaction produces carbon dioxide and releases heat. Hence, it is an **exothermic reaction**.
- **Option 4: Passage of CO2 through red hot carbon**:
- This reaction requires heat to proceed, as it absorbs heat from the surroundings to convert carbon dioxide into carbon monoxide. Therefore, it is an **endothermic reaction**.

4. **Conclusion**:
- The endothermic reaction among the options provided is **Option 4: Passage of CO2 through red hot carbon**.

### Final Answer:
The endothermic reaction is **Option 4: Passage of CO2 through red hot carbon**.