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

The first ionization energy for $Li$ is $5.4 \ eV$ and electron affinity of $Cl$ is $3.61 \ eV$. The $\Delta H$ (in $kJ/mol$) for the reaction $Li_{(g)} + Cl_{(g)} \to Li^{+}_{(g)} + Cl^{-}_{(g)}$ is (if resulting ions do not combine with each other) ($1 \ eV = 1.6 \times 10^{-19} \ J$,$N_A = 6.022 \times 10^{23} \ mol^{-1}$)

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

Which of the following represents the correct order of ionization enthalpy?
$(i) Ba < Sr < Ca$
$(ii) S^{2-} < S < S^{2+}$
$(iii) C < O < N$
$(iv) Mg < Al < Si$

Which blocks of the periodic table contain the representative elements?

State whether the following statements are true or false:
$(i)$ As the atomic number increases in a period,the nuclear charge increases,therefore the ionization enthalpy increases.
$(ii)$ As the metallic character of elements increases,the atomic radius generally increases.
$(iii)$ $Mn$ $(Z = 25)$ is a transition element. Although it is a $3d$-orbital element,its position in the periodic table is in the $4^{th}$ period.