In which of the following pairs, electron gain enthalpies of constituent elements are nearly the same or identical? (A) Rb and Cs (B) Na and K (C) Ar and Kr (D) I and At Choose the correct answer from the options given below

Step-by-step solution

Rb   &   Cs have nearly same electron gain enthalpy Their values are nearly = - 46   kJ / mol Ar   &   Kr also have same ΔH e . g . . Value is + 96   kJ / mol . Na   and   K have different values ( - 53   and   - 48   kJ / mol )   . And I   and   At   has   values   of   - 295   and   - 270   kJ / mol . As we move down the group value of electron gain enthalpy decreases, with few exceptions.