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.