Of the following acids,the one that is strongest is

$HClO_4$ is a stronger acid than $H_2SO_4$ due to which of the following reasons?
$1$. Oxidation state of $Cl$ in $HClO_4$ is $+7$ and that of $S$ in $H_2SO_4$ is $+6$.
$2$. $Cl$ is more electronegative than $S$.
$3$. $HClO_4$ is monobasic,whereas $H_2SO_4$ is dibasic.
$4$. $ClO_3$ part of $HClO_4$ can break $O-H$ bond more easily to liberate a proton than $SO_3$ part in $H_2SO_4$.

Identify the most acidic oxide among the following oxides based on their reaction.

Why do elements in the same group have similar physical and chemical properties?

Identify the statements which are not correct?
$(i)$ $ZnO, PbO, Sb_2O_3$ are neutral oxides.
(ii) $CO$ and $NO$ are amphoteric oxides.
(iii) $CrO_3, Mn_2O_7, V_2O_5$ are basic oxides.

Identify the correct order of acidic strengths of $CO_2, CuO, CaO, H_2O:-$