The correct statements about the oxoacids, ${\mathrm{HClO}}_4\mathrm{ }\mathrm{and}\mathrm{ }\mathrm{HClO}$ are,

• Correct answer
  A

  the conjugate base of ${\mathrm{HClO}}_4$ is weaker base than $\mathrm{HClO}$.
• Correct answer
  B

  the central atom in both ${\mathrm{HClO}}_4$ and $\mathrm{HClO}$is $\mathrm{ }{\mathrm{sp}}^3$ hybridized.
• C

  ${\mathrm{HClO}}_4$ is formed in the reaction between $\mathrm{ }{\mathrm{Cl}}_2\mathrm{ }\mathrm{and}\mathrm{ }{\mathrm{H}}_2\mathrm{O}$.
• Correct answer
  D

  ${\mathrm{HClO}}_4$ is more acidic than $\mathrm{HClO}$because of the resonance stabilization of its anion.

Hence, the correct answer is options: 'A', 'B', 'D'.