Question

Which of the following acids is the weakest? The acid is followed by its Ka value. HCOOH, 6.5 x 10-5 HCIO2, 1.1 x 10-2 HNO2, 4.6 x 10-4 HIO, 2.3 * 10-11 HF, 3.5 x 10-4

Answer 1

Whether an acid is strong or weak depends upon its dissociative constant $k_a$ . The dissociative constant tells us the extent of dissociation, if the given acid dissociates largely into its ions then it has a large value of $k_a$ whereas if the dissociation into constituent ions is less then the value of $k_a$ is also less.
In case of acids this dissociation into constituent ions also gives us H+ ions which are basically responsible for the acidity. Hence more $k_a$ means more H+ ions and a stronger acid.
In this question since HIO has the smallest value of $k_a$ it is the weakest acid among all.