Final answer:
HI is the most acidic compound among HI, HBr, HF, HCl, and H2O, reflecting the general trend that acidity increases as you move down the halogen group in the periodic table.
Step-by-step explanation:
The compound HI (hydroiodic acid) is the most acidic among the given options a. HI b. HBr c. HF d. HCl e. H2O. This is explained by considering the strength of hydrohalic acids, which generally increases as you move down the halogen group in the periodic table. The reasoning is based on the bond strength and size of the halide ions: as the size increases, the bond strength decreases, making it easier for the hydrogen-halide bond to dissociate and release H+ ions in solution. Therefore, the order of acidity generally increases as follows: HF < HCl < HBr < HI. Water (H2O), being a very weak acid, is less acidic than any of the hydrohalic acids listed.