With the help of the following reactions,arrange metals $A$,$B$,$D$,and $E$ in decreasing order of their reactivity:
$(I)$ $B + ANO_3 \to BNO_3 + A$
$(II)$ $A + HCl \to ACl + \frac{1}{2}H_2$
$(III)$ $D + ECl \to DCl + E$
$(IV)$ $D + HNO_3 \to H_2$ gas is not evolved

$HClO_4$ 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 $H_2SO_4$.

In the reaction $2Br^- + X_2 \to Br_2 + 2X^-$,$X_2$ is .......

The element with $Z = 120$ (not yet discovered) will be a/an:

The characteristics of elements $X$,$Y$ and $Z$ with atomic numbers,respectively,$33$,$53$ and $83$ are :

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