Correct option (a) greater than 1.30 Å
Explanation:
In BF3, there is back bonding in between fluorinc and boron due to presence of p-orbital in boron.
back bonding imparts double bond characteristics.
As BF3 forms adjuct the back bonding is no longer present and thus double bond characteristic disappears. Hence, bond becomes a bit longer than earlier ( 1.30 Å).