The ionization energy of an atom is the energy required to remove an electron from the atom. In the Bohr model, the ionization energy equals the energy difference between the lowest energy level n = 1 , in which the electron is closest to the nucleus, and the energy level n = [infinity] , which has an infinite radius.

The question is incomplete, the complete question is;

The ionization energy of an atom is the energy required to remove an electron from the atom. In the Bohr model, the ionization energy equals the energy difference between the lowest energy level n = 1 , In which the electron is closest to the nucleus, and the energy level n oo, which has an infinite radius. Compared to the ionization energy of hydrogen, the energy required to remove the electron from singly ionized helium is O two times greater. O four times greater. eight times greater. O one-half as great. O one-fourth as great.

four times greater

Explanation:

For a hydrogen atom, an ionization energy of 13.6 electron volts is required to eject its single electron from the lowest energy level all the way out of the atom.

The helium ground state contains only two 1s electrons. When one of these is removed, He^+ looks quite similar to H^+.

The energy required to remove the remaining helium electron should be; 4×(13.6eV)=54.4eV since the energy depends on the square of the nuclear charge.

it is easily magnetized.