The value of `Delta H` for the reaction
` X_2 (g) + 4Y_2 hArr 2XY_4(g) ` is less than zero.
Formation of `XY_4 (g) ` will be favoured at

Options

A. low pressure and low temperature
B. high temperature and low pressure
C. high pressure and low temperature
D. high temperature and high pressure.

Answer

To determine the conditions under which the formation of \( XY_4(g) \) is favored, we need to analyze the given reaction and the implications of the enthalpy change (\( \Delta H \)).

### Step-by-Step Solution:

1. **Identify the Reaction**:
The reaction is given as:
\[ X_2(g) + 4Y_2(g) \rightleftharpoons 2XY_4(g) \]

2. **Understand the Significance of \( \Delta H < 0 \)**:
The value of \( \Delta H \) being less than zero indicates that the reaction is exothermic. This means that heat is released when the reaction proceeds in the forward direction (from reactants to products).

3. **Consider the Effect of Temperature**:
- For exothermic reactions, the formation of products is favored at lower temperatures. This is because lowering the temperature shifts the equilibrium to the right (towards the formation of products) to release heat and counteract the change.
- Therefore, low temperature is favorable for the formation of \( XY_4(g) \).

4. **Analyze the Effect of Pressure**:
- According to Le Chatelier's principle, if the pressure is increased, the equilibrium will shift towards the side with fewer moles of gas.
- In this reaction, there are 5 moles of reactants (1 mole of \( X_2 \) and 4 moles of \( Y_2 \)) and 2 moles of products (2 moles of \( XY_4 \)).
- Since there are fewer moles of gas on the product side, increasing the pressure will favor the formation of \( XY_4(g) \).

5. **Combine the Conditions**:
- From the analysis, we conclude that the formation of \( XY_4(g) \) will be favored at low temperature and high pressure.

6. **Select the Correct Option**:
- Based on the conditions derived, the correct option is:
\[ \text{Option C: High pressure and low temperature} \]

### Summary:
The formation of \( XY_4(g) \) will be favored at high pressure and low temperature due to the exothermic nature of the reaction and the change in the number of moles of gas.