Ionization enthalpy of oxygen is 13.6 eV/atom. Energy required to ionize eight grams of oxygen is

Og→O+g , ∆iH=13.696.45 kJ ; 16 grams of oxygen require 13.696.45 kJ.  8 grams   of oxygen require ----'X' kJ. 'X'=13.696.45 kJ2=656 kJ ;