Which element among the following is most probable to have the following values?
$\Delta_i H_1 = 419 \ kJ \ mol^{-1}$
$\Delta_i H_2 = 3051 \ kJ \ mol^{-1}$
$\Delta_{eg} H = -48 \ kJ \ mol^{-1}$

Which blocks of the periodic table contain the representative elements?

Which of the following statements are correct?
$(i)$ First ionisation enthalpy of $He < $ Second ionisation enthalpy of $Li$.
$(ii)$ $Li$ has the highest second ionisation enthalpy.
$(iii)$ All $d$-block elements are transition elements.
$(iv)$ The only alphabet not found in the periodic table is the letter '$J$'.
$(v)$ Francium concentration is $\sim 10^{-18} \ ppm$ on Earth.

As we go from left to right in period $2$ of the periodic table,the gram atomic volume of the elements:

Which of the following order$(s)$ is/are correct?
$(1) Li < Be < B < C$ $(IE_1)$
$(2) Li < Na < K < Rb < Cs$ (Reducing power in gaseous state)
$(3) Li^{+} < Na^{+} < K^{+} < Rb^{+} < Cs^{+}$ (Ionic mobility in aqueous solution)
$(4) S > Se > Te > O$ $(EA)$

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