Which free-radical is most likely to result from the irradiation of CHFCLCF2CL? (basically which halogen atom is turned into a free radical)

I know the weakest bonds usually break first, but how am I supposed to know in this case?

Question

Which free-radical is most likely to result from the irradiation of CHFCLCF2CL? (basically which halogen atom is turned into a free radical) 

I know the weakest bonds usually break first, but how am I supposed to know in this case?

aaronq · Answer

The weakest bond will be the longest bond, the only two possible answers are F or Cl.

Think about electronegativity and covalent radius.