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(A): Thermal stability of group V hydrid...

(A): Thermal stability of group V hydrides decreases from `NH_(3)` to `BiH_(3)`
(R): The dissociation energy of M - H bond! increases down the group regularly 

A

Both A & R are true, R is the correct explanation of A

B

Both A & R are true, R is not correct explanation of A

C

A is true, R is false

D

A is false, R is true

Text Solution

AI Generated Solution

The correct Answer is:
To solve the question, we need to analyze both the assertion and the reason provided. ### Step 1: Understand the Assertion The assertion states that the thermal stability of group V hydrides decreases from NH₃ to BiH₃. - **Explanation**: As we move down the group from NH₃ (ammonia) to BiH₃ (bismuth hydride), the size of the central atom increases. This results in a longer bond length between the central atom (M) and hydrogen (H), which weakens the M-H bond. Consequently, the thermal stability of these hydrides decreases. ### Step 2: Understand the Reason The reason provided states that the dissociation energy of the M-H bond increases down the group regularly. - **Explanation**: This statement is incorrect. As we go down the group, the bond length increases due to the larger atomic size of the central atom, which leads to a decrease in the bond strength. Therefore, the dissociation energy of the M-H bond actually decreases down the group, contradicting the reason given. ### Step 3: Conclusion Based on the analysis: - The assertion (A) is true because the thermal stability of group V hydrides does decrease from NH₃ to BiH₃. - The reason (R) is false because the dissociation energy of the M-H bond does not increase; it decreases down the group. Thus, the correct answer is that the assertion is true, but the reason is false. ### Final Answer: **Assertion (A) is true, and Reason (R) is false.** ---
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