Which one of the following sets of ions represents the collection of isoelectronic species?

Match List-$I$ with List-$II$:

List-$I$	List-$II$
$A$. $Al^{3+} < Mg^{2+} < Na^{+} < F^{-}$	$I$. Ionisation Enthalpy
$B$. $B < C < O < N$	$II$. Metallic character
$C$. $B < Al < Mg < K$	$III$. Electronegativity
$D$. $Si < P < S < Cl$	$IV$. Ionic radii

Choose the correct answer from the options given below:

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

Nitrogen has positive electron gain enthalpy whereas oxygen has negative. However,oxygen has lower ionisation enthalpy than nitrogen. Explain.

Which of the following statements is $NOT$ correct?

Which group is called the buffer group of the periodic table?