Which of the following reaction can be used to define the heat of formation of `CO_(2)(g)` ?

Options

A. C (graphite) `+O_(2)(g)to CO_(2)(g)`
B. `CH_(4)(g)+2O_(2)(g)to CO_(2)(g)+2H_(2)O(l)`
C. `CO(g)+1//2O_(2)(g)to CO_(2)(g)`
D. `C_(6)H_(6)(l)+7(1)/(2)O_(2)(g)to 6CO_(2)(g)+3H_(2)O(l)`

Answer

To determine which reaction can be used to define the heat of formation of \( CO_2(g) \), we need to understand what heat of formation means.

### Step-by-Step Solution:

1. **Definition of Heat of Formation**:
- The heat of formation (\( \Delta H_f \)) of a compound is defined as the heat change that occurs when one mole of the compound is formed from its constituent elements in their standard states.

2. **Identify the Constituent Elements of \( CO_2 \)**:
- The constituent elements for carbon dioxide (\( CO_2 \)) are carbon (C) and oxygen (O).
- In its standard state, carbon is typically found as graphite, and oxygen is found as a diatomic gas (\( O_2 \)).

3. **Write the Formation Reaction**:
- The formation reaction for \( CO_2(g) \) from its elements can be written as:
\[ C(s) + O_2(g) \rightarrow CO_2(g) \]
- This reaction represents the formation of one mole of \( CO_2 \) from one mole of carbon (in solid form) and one mole of oxygen (in gaseous form).

4. **Select the Correct Reaction**:
- Among the given options, the reaction that matches the formation of \( CO_2(g) \) from its elements is the one that shows carbon and oxygen as reactants leading to the formation of \( CO_2(g) \).

### Conclusion:
- The correct reaction that can be used to define the heat of formation of \( CO_2(g) \) is:
\[ C(s) + O_2(g) \rightarrow CO_2(g) \]