The B-F bond in `BF_(3)` is shorter in length that the B-F bond in `BF_(4)^(-)`- explainwith reasons.

Explanation

The outermost shell of the central B-atom of `BF_(3)` molecule contains six electrons. Since B-atom has an incomplte octet, it participates in resonance with the F-atoms to complete its octet. As a result, the B-F bonds acquire partial double bond character. on the other hand, the B-atom in `BF_(4)^(-)` ion has a completely filled octet filled up and so it does not participate in resonance. therefore, B-F bonds do not assume double bond character. hence the B-F bonds in `BF_(3)` molecule is shorter in length than that in `BF_(4)^(-)` ion.