Assertion (A): Nitric oxide on heating becomes yellowish brown in colour.
Reason (R): On oxidation NO oxidises into yellow brown coloured `NO_2`.

Options

A. Both A and Rare true and R is the correct explanation of A
B. Both A and Rare true but Ris not the correct explanation of A
C. A is true but R is false
D. A is false but R is true

Explanation

**Step-by-Step Solution:**

1. **Understanding the Assertion (A)**: The assertion states that "Nitric oxide on heating becomes yellowish brown in colour." This is a claim about the physical change that occurs when nitric oxide (NO) is heated.

2. **Understanding the Reason (R)**: The reason provided is that "On oxidation, NO oxidises into yellow brown coloured NO2." This implies that when nitric oxide is exposed to oxygen (oxidized), it transforms into nitrogen dioxide (NO2), which is known to have a yellowish-brown color.

3. **Analyzing the Reaction**: When nitric oxide (NO) is heated in the presence of oxygen, it reacts to form nitrogen dioxide (NO2):
\[ 2NO + O_2 \rightarrow 2NO_2 \]
This reaction indicates that nitric oxide is oxidized to nitrogen dioxide.

4. **Color Change**: Nitrogen dioxide (NO2) is indeed a yellowish-brown gas. Therefore, when nitric oxide is heated and oxidized to nitrogen dioxide, the resulting color change from colorless (NO) to yellowish-brown (NO2) supports the assertion.

5. **Conclusion**: Both the assertion and the reason are true. The reason correctly explains why the assertion is true. Thus, we can conclude that both the assertion and reason are valid and related.

**Final Answer**: Both Assertion (A) and Reason (R) are true, and the reason is the correct explanation for the assertion.

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