The number of alkali metal(s), from Li, K, Cs, Rb having ionization enthalpy greater than 400 $kJ mo

Question

The number of alkali metal(s), from Li, K, Cs, Rb having ionization enthalpy greater than 400 $kJ mol^{-1}$ and forming stable super oxide is ______

Professor PC Thomas Classes · Answer

K, Rb, Cs form stable superoxides. Their IEs are K (419), Rb (403), Cs (376). Thus, only K and Rb have IE > 400. Answer is 2.