Question

(A) Strength of acidic character of oxyacid lies in the following sequence:
$HCI{O_4} > HBr{O_4} > HI{O_4}$
(R) Greater is the oxidation state of a halogen, more is the acidic character of its oxyacid.
(a) Both (R) and (A) are true and reason is the correct explanation of assertion.
(b) Both (R) and (A) are true but the reason is not the correct explanation of the assertion.
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) and reason (R) both are false.
(e) Assertion (A) is false but reason (R) is true.

Answer 1

Hint: An oxyacid, Oxo acid is an acid that contains oxygen. It is a compound that contains hydrogen, oxygen, and at least one other element, with at least one hydrogen atom bond to oxygen that can dissociate to produce ${H^ + }$ cation and the anion. All halogen can Oxo acid and their acidic strength depends on the electronegativity of the central atom (Halogen).

Complete answer:
> $HCI{O_4}$, $HBr{O_4}$ and $HI{O_4}$ are oxoacids having central atom CI, Br, I respectively and the oxidation state of all central atom have + 7.
> The acidic strength of oxoacids depends on the electronegativity. As the electronegativity of halogen decreases, the tendency of $X{O_4}$ group (where X is halogen) to withdraw of the O - H bond toward itself decreases and hence the acid strength of acid decreases.
> The electronegativity decreases top to bottom in a group. Thus acidic strength decreases in the order $HCI{O_4} > HBr{O_4} > HI{O_4}$.
Hence the first statement (A) is correct.
> Acidic strength of Oxoacids of the same halogen increases with increase the oxidation number of the halogen. This can be explained on the basis of the relative stability of the anion left after removal of a proton. Now greater the number of oxygen atoms in the anion, greater will be the dispersal of the negative charge through $p\pi - d\pi$ bonding. Hence greater stability of the anion.
> Hence the second statement is also correct and it is also the correct explanation of option (A).

So the correct answer is (A).

Note: Fluorine has a very small size and high electronegative. Therefore, it forms only one Oxo acid, HOF which is known as hypofluorous acid. Fluorine cannot act as a central atom in higher oxoacids.