Properties and Characteristics of Perchloric and Hypochlorous Oxoacids

To determine the correct statements regarding the oxoacids $\text{HClO}_4$ (perchloric acid) and $\text{HClO}$ (hypochlorous acid), we evaluate each option individually:

1. Statement (A): Hybridization of the central atom

• For $\text{HClO}_4$: The central chlorine atom forms three double bonds with oxygen atoms ($\text{Cl}=\text{O}$) and one single bond with an $-\text{OH}$ group ($\text{Cl}-\text{OH}$). Chlorine has $4$ $\sigma$-bonds and $0$ lone pairs. $\text{Steric Number} = 4 + 0 = 4 \implies sp^3 \text{ hybridization}$
• For $\text{HClO}$: Considering the chlorine atom, it is bonded to one oxygen atom via a single $\sigma$-bond and retains $3$ lone pairs. $\text{Steric Number} = 1 + 3 = 4 \implies sp^3 \text{ hybridization}$ (Alternatively, considering oxygen as the central atom, it forms $2$ $\sigma$-bonds with $\text{H}$ and $\text{Cl}$ and has $2$ lone pairs, giving a steric number of $2 + 2 = 4$, which also corresponds to $sp^3$ hybridization).

Thus, Statement (A) is correct.

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2. Statement (B): Relative acidity and resonance stabilization

• The ionization of $\text{HClO}_4$ gives the perchlorate anion ($\text{ClO}_4^-$): $\text{HClO}_4 \rightleftharpoons \text{H}^+ + \text{ClO}_4^-$ In $\text{ClO}_4^-$, the negative charge is delocalized equally over all four oxygen atoms through resonance across four equivalent canonical structures.
• The ionization of $\text{HClO}$ gives the hypochlorite anion ($\text{ClO}^-$): $\text{HClO} \rightleftharpoons \text{H}^+ + \text{ClO}^-$ In $\text{ClO}^-$, the negative charge remains localized on a single oxygen atom without any resonance stabilization.

Because higher conjugate base stabilization increases acid strength, $\text{HClO}_4$ is a significantly stronger acid than $\text{HClO}$.

Thus, Statement (B) is correct.

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3. Statement (C): Reaction of $\text{Cl}_2$ with $\text{H}_2\text{O}$

• The reaction of chlorine gas with water is a disproportionation reaction yielding hydrochloric acid ($\text{HCl}$) and hypochlorous acid ($\text{HClO}$): $\text{Cl}_2 + \text{H}_2\text{O} \rightleftharpoons \text{HCl} + \text{HClO}$
• It does not produce perchloric acid ($\text{HClO}_4$).

Thus, Statement (C) is incorrect.

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4. Statement (D): Basic strength of the conjugate base of $\text{HClO}_4$ relative to $\text{H}_2\text{O}$

• According to the Brønsted-Lowry theory, a stronger acid has a weaker conjugate base.
• The $pK_a$ values for $\text{HClO}_4$ and $\text{H}_3\text{O}^+$ are approximately: $pK_a(\text{HClO}_4) \approx -10, \quad pK_a(\text{H}_3\text{O}^+) \approx -1.74$
• Since $\text{HClO}_4$ is a much stronger acid than $\text{H}_3\text{O}^+$, its conjugate base ($\text{ClO}_4^-$) is a weaker base than the conjugate base of $\text{H}_3\text{O}^+$ (which is $\text{H}_2\text{O}$).

Thus, Statement (D) is correct.

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Conclusion

The correct options are A, B, and D.