The correct option is A BI3>BBr3>BCl3>BF3
As we go down the group, the size of the atom increases. Hence, we can say that the size and hence the mass of Boron trihalides increases as we go down the group. This gives us the estimate that the van der Waal's forces increase as we go down the group. Hence, the boiling point increases down the group. So, the correct order is: BI3>BBr3>BCl3>BF3