$Be$ and $Al$ resemble in:

$HClO_4$ 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 $H_2SO_4$.

Among the following,the least and most metallic elements will be respectively:
$(I) [He] 2s^1$
$(II) [Kr] 5s^2 4d^{10} 5p^5$
$(III) [Xe] 6s^1$
$(IV) [He] 2s^2 2p^5$

The correct order of relative basic character of $NaOH$,$Mg(OH)_2$ and $Al(OH)_3$ is

The electronic configuration of an atom $A$ is $1s^2, 2s^2 2p^6, 3s^2 3p^6 3d^{10}, 4s^2 4p^3$. The chemistry of $A$ is therefore likely to be similar to that of:

Which of the following is a normal element?