`2CO_((g))+O_(2(g))rarr 2CO_(2(g))+X` KJ In the above equation X KJ refers to :

Options

A. Heat of formation of `CO_(2)`
B. Heat of vapourisation
C. Heat of reaction
D. Heat of sublimation

Answer

To solve the question regarding the reaction \(2CO_{(g)} + O_{2(g)} \rightarrow 2CO_{2(g)} + X\) KJ, we need to determine what \(X\) refers to in this context.

### Step-by-Step Solution:

1. **Identify the Reaction**: The reaction given is between carbon monoxide (CO) and oxygen (O2) to produce carbon dioxide (CO2). The reaction can be represented as:
\[ 2CO_{(g)} + O_{2(g)} \rightarrow 2CO_{2(g)} + X \text{ KJ} \]

2. **Understand the Terms**: In thermodynamics, \(X\) typically represents the energy change associated with the reaction. This can be in the form of heat released or absorbed during the reaction.

3. **Evaluate the Options**:
- **Heat of Formation**: This refers to the energy change when one mole of a compound is formed from its elements. Since we are dealing with a reaction involving multiple moles, this is not applicable.
- **Heat of Vaporization**: This is the energy required to convert a liquid into a gas. Since our reaction does not involve a phase change from liquid to gas, this is also not applicable.
- **Heat of Reaction**: This is the energy change that occurs during a chemical reaction. In this case, it refers to the heat released when CO reacts with O2 to form CO2. This is likely the correct answer.
- **Heat of Sublimation**: This is the energy required to convert a solid directly into a gas. Since there are no solids in this reaction, this option is not applicable.

4. **Conclusion**: Based on the evaluation of the options, the correct interpretation of \(X\) in the reaction is the **heat of reaction**. Therefore, \(X\) refers to the energy change associated with the reaction, which is typically expressed in kilojoules (KJ).

### Final Answer:
**X KJ refers to the heat of reaction.**