Question

Assertion :The canonical forms in which the negative charge resides on the electronegative atoms contribute more, but in $B{F}_3$ the $p\pi -p\pi$ back bonding places a positive charge on $F$ which is more electronegative than $B$ Reason: This disfavor is compensated due to the formation of an additional $\pi -bond$

Read the above assertion and reason and choose the correct option regarding it.

• A.
  Assertion is true, Reason is true and Reason is correct explanation for Assertion
• B. Assertion is true, Reason is true and Reason is not the correct explanation for Assertion
• C. Assertion is true, Reason is false
• D. Assertion is false, Reason is true

Answer 1

The correct option is A

Assertion is true, Reason is true and Reason is correct explanation for Assertion

The canonical forms in which the negative charge resides on the electronegative atoms contribute more, but in $B{F}_3$ the $p\pi -p\pi$ back bonding places a positive charge on $F$ which is more electronegative than $B$. This should not be favored. But since, additional pi bond is formed, this disfavor is compensated.
Hence, Assertion is true, Reason is true and Reason is correct explanation for Assertion.