Arrange in terms on increasing ionization energy: H, K, Si, O

K < Si < O < H

Explanation:

The ionization energy is regarded to be the amount of energy required to remove an electron in an atom from its ground state. The factor that determines the Ionization energy atomic radius. This is because the larger the atomic radius, the smaller the Ionization energy because of the shielding effect or screening effect of the inner shell electrons.  Across the period, the ionization energy increases progressively from left to right due to decreasing atomic radii caused by the increased nuclear charge. Also, down the period the ionization energy decreases because of increasing atomic radii and increasing shielding effect or screening effect of the inner shell electrons.

So, the increasing order of Ionization energy of the given elements are:

K < Si < O < H