(A) : For `N_(2) + 3H_(2) hArr 2NH_(3). Delta ` H =-Q KJ, high pressure yiclds more Ammonia
(R) According to Lechatlier's principle, increase of pressure shifts equilibrium in a direction that proceeds in decrease in number of moles.

Answer

To solve the problem, we will analyze the assertion and reason provided in the question step by step.

### Step 1: Understand the Reaction
The given reaction is:
\[ N_2 + 3H_2 \rightleftharpoons 2NH_3 \]

### Step 2: Identify Moles of Reactants and Products
- On the left side (reactants), we have:
- 1 mole of \( N_2 \)
- 3 moles of \( H_2 \)

Total moles on the left = \( 1 + 3 = 4 \) moles.

- On the right side (products), we have:
- 2 moles of \( NH_3 \)

Total moles on the right = \( 2 \) moles.

### Step 3: Analyze the Effect of Pressure on Equilibrium
According to Le Chatelier's principle, if a system at equilibrium is subjected to a change in pressure, the equilibrium will shift in the direction that reduces the pressure. This typically means shifting towards the side with fewer moles of gas.

### Step 4: Apply Le Chatelier's Principle
In our reaction:
- The left side has 4 moles of gas.
- The right side has 2 moles of gas.

When we increase the pressure, the equilibrium will shift towards the side with fewer moles of gas to counteract the change. In this case, it will shift to the right, producing more \( NH_3 \).

### Step 5: Conclusion
- The assertion states that high pressure yields more ammonia, which is true because the equilibrium shifts to the right (towards the production of \( NH_3 \)).
- The reason states that an increase in pressure shifts equilibrium in a direction that decreases the number of moles, which is also true and correctly explains the assertion.

### Final Answer
Both the assertion and reason are correct, and the reason is the correct explanation of the assertion.

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