In the reaction, `2SO_(2)(s)+O_(2)(g) hArr 2SO_(3)(g)+X cal`, most favourable conditions of temperature and pressure for greater yield of `SO_(3)` are

Options

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

Explanation

To determine the most favorable conditions of temperature and pressure for greater yield of SO3 in the reaction:

\[ 2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g) + X \text{ cal} \]

we can analyze the reaction using Le Chatelier's principle and the characteristics of the reaction.

### Step 1: Identify the nature of the reaction
The reaction involves the conversion of sulfur dioxide (SO2) and oxygen (O2) into sulfur trioxide (SO3). The reaction is exothermic, meaning it releases heat.

### Step 2: Analyze the moles of gas
In the reaction:
- On the reactant side, we have 2 moles of SO2 and 1 mole of O2, totaling 3 moles of gas.
- On the product side, we have 2 moles of SO3.

### Step 3: Consider the effect of pressure
According to Le Chatelier's principle, increasing the pressure of a gaseous reaction will shift the equilibrium towards the side with fewer moles of gas. Here, since we have 3 moles of gas on the reactant side and 2 moles on the product side, increasing the pressure will shift the equilibrium to the right, favoring the production of SO3.

### Step 4: Consider the effect of temperature
Since the reaction is exothermic, lowering the temperature will favor the formation of products. According to Le Chatelier's principle, if the temperature is decreased, the equilibrium will shift in the direction that produces heat (the forward direction in this case), thus favoring the production of SO3.

### Conclusion
To achieve a greater yield of SO3, the conditions should be:
- **Low temperature** (to favor the exothermic reaction)
- **High pressure** (to favor the side with fewer moles of gas)

Thus, the most favorable conditions for greater yield of SO3 are **low temperature and high pressure**.

### Final Answer
The correct option is: **Low temperature and high pressure.**

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