Why is the ionization potential of singly ionized helium about 4 times the ionization potential of hydrogen

Question

Also... If the ionisation potential of hydrogen is 13.6 eV, what is the energy, wavelength and frequency of the first transition of the hydrogen Paschen series?

Many Thanks for any help!!

Answer 1

the ionization potential of helium is greater than that of hydrogen because they have their outermost electrons in the same energy level but helium has one more proton in its nucleus than hydrogen. this enables the positve nucleus to hold in the electron with more force and so the ionisation potential is higher