Which one of the following molecules would be most polar?
(a) hf
(b) hi
(c) hbr
(d) hcl and h2

This question is quite a controversial one, because three of the options represented above are very similar, but due to the fact that there is a HF, which is even more polar that water, it is getting clear. So, the right answer is definitely the first option, because HF belongs to acids that are very polar compounds.