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

Step-by-step solution

The super oxide O 2 - ion is stable only in the presence of large cations K , Rb , Cs . K , Rb have IE 1 > 400   kJ / mol from the table below. Ionisation enthalpy decreases down the group as metallic character increases. Metal Li Na K Rb Cs IE ( KJ / mol ) 520 496 419 403 376