All three of the boron-fluorine single bonds in bf3 are polar. in which direction should the polarity arrows point?

The direction of polarity arrow should be from B atom to F atom

Explanation:

F atom has higher electronegativity than B atom.

Therefore the bonding electron between B and F atom will be polarized and become more concentrated towards F atom. Because F atom pulls bonding electrons towards itself more due to it's higher electronegativity.

Hence F atom gets a partial negative charge and B atom gets a partial positive charge.

The polarity arrows are generally pointed from positively charged center to negatively charged center.

So, the direction of polarity arrow should be from B atom to F atom.

Please find the picture below.