Energy required to remove e−from singly ionized helium atom =12(13.6)Z2=54.4eV (∵Z=2) Energy required to remove e−from helium atom =xeV According to question, 54.4eV=2.2x⇒x =24.73eV Therefore, energy required to ionize helium atom =(54.4+24.73)eV=79.12eV