For an acid-base reaction, what is the reacting species in the following acid: Hydriodic acid? How do you determine this?

##HI## undergoes almost complete ionization in water. How do you determine this? By experiment.

Except for ##HF##, ALL of the hydrogen halides in water are strongly acidic: ##HI>HBr>HCl##. This difference in acidity is due to the weaker bond overlap of the higher halides, and also to the entropy effect of the smaller halide ions.