A : The bond angle of `NH_3` is greater than `BiH_(3)` .
R : 'Bi' is metal while N is non - metal .

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion , then mark (1)
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion , then mark (2)
C. If Assertion is true statement but Reason is false , then mark (3)
D. If both Assertion and Reason are false statements , then mark (4)

Answer

To solve the assertion-reason question, we need to analyze both the assertion (A) and the reason (R) provided.

### Step 1: Analyze the Assertion (A)
The assertion states that "the bond angle of NH3 is greater than BiH3."

- **NH3 (Ammonia)**: The molecular geometry of ammonia is trigonal pyramidal due to the presence of one lone pair of electrons on nitrogen. The bond angle in NH3 is approximately 107 degrees.

- **BiH3 (Bismuth Hydride)**: The molecular geometry of bismuth hydride is also trigonal pyramidal, but bismuth is a larger atom compared to nitrogen. The bond angle in BiH3 is approximately 90 degrees.

Since the bond angle in NH3 (107 degrees) is indeed greater than that in BiH3 (90 degrees), the assertion is **correct**.

### Step 2: Analyze the Reason (R)
The reason states that "Bi is metal while N is non-metal."

- **Metallic Character**: As we move down the group in the periodic table, the metallic character increases. Nitrogen (N) is a non-metal, while bismuth (Bi) is classified as a metal.

This statement is also **correct**. However, it does not directly explain why the bond angle in NH3 is greater than that in BiH3. The difference in bond angles is primarily due to the size and electron repulsion effects rather than the metallic character of the elements.

### Conclusion
Both the assertion and the reason are correct, but the reason is not the correct explanation for the assertion. Therefore, the final answer is:

- **Assertion (A)**: True
- **Reason (R)**: True
- **Conclusion**: R is not the correct explanation of A.