Which of the following oxoacids is the weakest acid ?

Options

A. `HCIO_(4)`
B. `HCIO_(3)`
C. `HCIO_(2)`
D. `HCIO`

Answer

D

Explanation

These oxacids have the same central atom but different numbers of attached groups:

Within this group, the acid strength increases as the oxidation number of the central atom increases. In the above series, the ability of chlorine to draw electrons away form the OH group (thus, making the O-H bond more polar) increses with the number of electronegative O atoms attached to CI. Thus, `HCIO_(4)` is the strongest acid because it has the largest number of O atom attached to CI, and the acid strength decreases as follows:
`HCIO_(4)gtHCIO_(3)gtHCIO_(2)gtHCIO`
Acids strengths of most ternary acids containing the same central element increase with increaseing oxidation state of the central element and with increasing number of oxygen atoms. As the oxidation number of an atom becomes larger, its ability to draw electrons in a bond toward itself increases.