Choose the correct statement$(s)$.

Which of the following statements are true?
$A.$ Unlike $Ga$ that has a very high melting point,$Cs$ has a very low melting point.
$B.$ On Pauling scale,the electronegativity values of $N$ and $Cl$ are not the same.
$C.$ $Ar$,$K^{+}$,$Cl^{-}$,$Ca^{2+}$,and $S^{2-}$ are all isoelectronic species.
$D.$ The correct order of the first ionization enthalpies of $Na$,$Mg$,$Al$,and $Si$ is $Si > Al > Mg > Na$.
$E.$ The atomic radius of $Cs$ is greater than that of $Li$ and $Rb$.
Choose the correct answer from the options given below

The isoelectronic set of ions is

$A, B$,and $C$ are hydroxy-compounds of the elements $X, Y$,and $Z$ respectively. $X, Y$,and $Z$ are in the same period of the periodic table. $A$ gives an aqueous solution of $pH < 7$. $B$ reacts with both strong acids and strong alkalis. $C$ gives an aqueous solution which is strongly alkaline.
Which of the following statements is / are true?
$I$: The three elements are metals.
$II$: The electronegativities decrease from $X$ to $Y$ to $Z$.
$III$: The atomic radius decreases in the order $X, Y$,and $Z$.
$IV$: $X, Y$,and $Z$ could be phosphorus,aluminium,and sodium respectively.

Match the following elements,given as hints to their first,second ionization enthalpies and electron gain enthalpies.

List-$I$	List-$II$
$i)$ Most reactive non-metal	$A$. $\Delta H_1=419, \Delta H_2=3051, \Delta_{Eg} H=-48$
$ii)$ Most reactive metal	$B$. $\Delta H_1=1681, \Delta H_2=3374, \Delta_{Eg} H=-328$
$iii)$ Least reactive element	$C$. $\Delta H_1=738, \Delta H_2=1451, \Delta_{Eg} H=-40$
$iv)$ Metal forming binary halide	$D$. $\Delta H_1=3272, \Delta H_2=5251, \Delta_{Eg} H=+48$

Match the following and select the correct option:

List-$I$	List-$II$
$(A)$ Ionization enthalpy	$(i)$ $P < Si < Mg < Na$
$(B)$ Metallic character	$(ii)$ $I < N < O < F$
$(C)$ Electron gain enthalpy	$(iii)$ $B < Be < C < O < N$
$(D)$ Electronegativity	$(iv)$ $I < Br < F < Cl$