Which of the following acids is the weakest?

Chlorine cannot be used:

The correct statement$(s)$ about the oxoacids,$HClO_4$ and $HClO$,is(are):
$[A]$ $HClO_4$ is more acidic than $HClO$ because of the resonance stabilization of its anion.
$[B]$ $HClO_4$ is formed in the reaction between $Cl_2$ and $H_2O$.
$[C]$ The central atom in both $HClO_4$ and $HClO$ is $sp^3$ hybridized.
$[D]$ The conjugate base of $HClO_4$ is a weaker base than $H_2O$.

$A$ radioactive element resembling iodine in properties is

Noble metals,like gold and platinum,are soluble in which of the following mixtures?

Which member of the halogen $(X_2)$ group does not exhibit a positive oxidation state $(X_2^+)$?