In BF3 , B-F bond length is 1.30 Å , When BF3 is allowed to be treated with Me3N , It forms an adduct , [Me3N- BF3] The bond length of B-F in the adduct is (1)Greater than 1.30Å(2)Smaller than 1.30 Å(3)Equal to 1.30Å(4)None of these

Dear Shivansh,
In case of BF3, there is back bonding and due to that, double bond characteristics is present which shortens the bond length.
But when there is adduct formation, there is no scope of back bonding hence bond length increases.
Regards
Arun (askIITians forum expert)