Assertion (A) : A change of pressure has no effect in case of the equilibrium,
`N_(2)(g)+O_(2)(g) hArr 2NO(g)`
Reason (R) : The reaction,
`N_(2)(g)+O_(2)(g) hArr 2NO(g)` is highly exothermic reaction

Options

A. If both (A) and (R) are correct, and (R) is the correct explanation for (A)
B. If both (A) and (R) are correct, but (R) is not the correct explanation of (A)
C. If (A) is correct, but (R) is incorrect
D. If (A) is incorrect, but (R) is correct.

Answer

To solve the question regarding the assertion and reason about the equilibrium reaction \( N_2(g) + O_2(g) \rightleftharpoons 2NO(g) \), we will analyze both the assertion (A) and the reason (R) step by step.

### Step 1: Analyze the Assertion (A)
The assertion states that a change of pressure has no effect on the equilibrium of the reaction \( N_2(g) + O_2(g) \rightleftharpoons 2NO(g) \).

- **Moles of Reactants**: In the reaction, there are 1 mole of \( N_2 \) and 1 mole of \( O_2 \), totaling 2 moles of reactants.
- **Moles of Products**: The products consist of 2 moles of \( NO \).

Since the number of moles of reactants (2 moles) is equal to the number of moles of products (2 moles), according to Le Chatelier's principle, a change in pressure will not affect the position of equilibrium. Thus, the assertion is **correct**.

### Step 2: Analyze the Reason (R)
The reason states that the reaction \( N_2(g) + O_2(g) \rightleftharpoons 2NO(g) \) is a highly exothermic reaction.

- **Exothermic vs. Endothermic**: An exothermic reaction releases heat, while an endothermic reaction absorbs heat. The formation of \( NO \) from \( N_2 \) and \( O_2 \) actually requires energy input to break the strong triple bond in \( N_2 \) and the double bond in \( O_2 \). Therefore, this reaction is **endothermic**, not exothermic.

Since the reason provided is incorrect, we conclude that the reason (R) is **false**.

### Conclusion
- **Assertion (A)**: Correct
- **Reason (R)**: Incorrect

Thus, the final answer is that the assertion is correct, but the reason is incorrect. The correct option is that A is correct, and R is incorrect.