High pressure and high temperature will be favourable conditions for a high equilibrium yield in the reaction

Options

A. `2Cl_2O_7 (g) to 2Cl_2(g)+7O_2(g)+126.8` kcal
B. `N_(2(g))+3H_(2(g)) to 2NH_(3(g)) + 22.08 kcal `
C. `Cl_(2(g)) + 2O_(2(g)) to 2ClO_(2(g)) `-49.4 kcal
D. `2NF_(3(g)) to N_(2(g)) + 3F_(2(g)) ` - 54.4 kcal

Explanation

To determine which reaction is favored by high pressure and high temperature conditions for achieving a high equilibrium yield, we will analyze the given reactions based on their enthalpy changes and the number of moles of reactants and products.

### Step-by-Step Solution:

1. **Identify the nature of the reactions**:
- The first step is to analyze each reaction based on the provided enthalpy changes (kcal) and the number of moles of reactants and products.

2. **Analyze the first reaction**:
- The first reaction has an enthalpy change of +126.8 kcal, indicating it is an **endothermic reaction** (heat is absorbed).
- For endothermic reactions, **high temperature** is favorable for the forward reaction, but **high pressure** does not necessarily favor it unless the number of moles changes favorably.

3. **Analyze the second reaction**:
- The second reaction has an enthalpy change of +22.8 kcal, which also indicates it is an **endothermic reaction**.
- Similar to the first reaction, high temperature is favorable, but we need to check the moles of reactants and products to assess the effect of pressure.

4. **Analyze the third reaction**:
- The third reaction has an enthalpy change of -49.4 kcal, indicating it is an **exothermic reaction** (heat is released).
- For exothermic reactions, **low temperature** is favorable.

5. **Determine the moles of reactants and products**:
- For the third reaction, we have:
- Reactants: Cl2 + 2O2 (3 moles total)
- Products: 2ClO2 (2 moles total)
- Since the number of moles of products (2) is less than that of reactants (3), high pressure will favor the formation of products.

6. **Conclusion**:
- High pressure and high temperature conditions are favorable for the third reaction (Cl2 + 2O2 ⇌ 2ClO2) because:
- It is exothermic, and while high temperature is not favorable, the reduction in volume due to fewer moles of products makes high pressure favorable.
- Therefore, the answer is that the third reaction is favored under high pressure and high temperature conditions.

### Final Answer:
The reaction that is favored by high pressure and high temperature conditions for a high equilibrium yield is the third reaction: Cl2 + 2O2 ⇌ 2ClO2.