Which of the following oxocids is the strongest acid ?

Options

A. HCIO
B. HBrO
C. HIO
D. All are equally strong

Answer

A

Explanation

These oxacids have different central atoms which are from the same group of the periodic table and which have the same oxidation number. Within this group of oxoacids, the strengths of the acids increse with increasing electrnegativity of the central atom:

All these acids have the same structure, and all the haligens have the same oxidation number `(+1)`. Since CI is more electronegative than Br and I, it attracts the electron pair it shares with the oxygen (in the CI-O bond) to a greater extent than Br or does. Consequently, the O-H bond is more polar in hypochlirous acid (HCIO) and ionizes more readily. Thus, the relative acid strengths are
`HCIOgtHBrOgtHIO`
For most ternary acids sontaning different element in the same oxidation state dorm the same group in the periodic table, acid strengths increase with increaseing electronegativity of the central element. Since the electronegativity decreases form CI to I, the polarity of the X-O bond (where X denotes a halogen atom) increases form HCIO to HIO, and the polarity of the O-H bond decreases form HCIO to HIO.