The correct option is A BF3
For pπ−dπ back bonding, one atom must have a lone pair in its p-orbital and the other must have vacant d-orbitals.
a) In O(SiH3)2, oxygen has a lone pair in its p-orbital and Si has vacant d-orbitals. So, O(SiH3)2 has pπ−dπ back bonding.
b) In PF3, fluorine has a lone pair in its p-orbital and P has vacant d-orbitals. So, PF3 has pπ−dπ back bonding.
c) In AsF3, fluorine has a lone pair in its p-orbital and As has vacant 4d-orbitals. So, AsF3 has very poor pπ−dπ back bonding.
d) In BF3, fluorine has a lone pair in its p-orbital and Boron has vacant p-orbitals. So, BF3 has pπ−pπ back bonding and not pπ−dπ back bonding.