Which is the weakest acid from the following. So here we have HF, HCL, HI, HBR or all are equal if we look at the periodic table. Remember we're looking at the non hydrogen element found within the binary acid. So we need to compare fluorine, chlorine, bromine and iodine to one another when they're in the same group.
Remember we look at atomic radius and we say the higher the atomic radius then the more acidic the acid. If we look, iodine would have the largest atomic radius out of the four elements. As a result of this, HI would be the strongest acid, but here we're looking for the weakest.
The one with the smallest atomic radius would be fluorine, so HF would be our weakest acid. So here option A is the correct answer.