Question

Why is iodic acid a stronger acid than nitric acid?

Answer 1

Are you sure you mean iodic acid, `HIO_3`?

Explanation:

This site lists `pK_a` of iodic acid at `0.75`. On the other hand, this site lists `pK_a` of nitric acid at `-1.4`. So given these metrics, nitric acid is a stronger acid than iodic acid.

You might mean to compare periodic acid, `HIO_4`, which should be a stronger acid than iodic acid (why?). For comparison, this site lists `pK_a` of `HClO_4` at `-15.2`. `HIO_4` should be more strongly acidic (I could not find the metrics for this acid). Can you quote the oxidation state of iodine in its oxo-acids?

Note that as a scientist, you should always look at the metrics. Of course, you don't know them off the top of your head (I certainly did not). But you should be able to interpret the metrics to make an argument.