The correct statement is:
$\text{BF}_3$ is the strongest Lewis acid among the other boron halides.
$\text{BF}_3$ is the weakest Lewis acid among the boron halides.
There is maximum $\pi p - \pi p$ back bonding in $\text{BF}_3$.
There is minimum $\pi p - \pi p$ back bonding in $\text{BF}_3$.
