Answer:1. Ionization
2. columns
Explanation:
1. Ionization energy is the energy required to remove the outermost electron from an isolated gaseous atom.
In a period or row, the ionization energy increases as we move down as the size decreases and thus the valence shell moves closer to the nucleus and thus is difficult to remove.
In a group or column, the ionization energy decreases as we move down as the size increases and thus the valence shell moves farther from nucleus and thus is easier to remove.
2. The elements are arrange in order of increasing atomic numbers in which elements with similar properties are present at regular intervals.
The rows of the periodic table are called as rows and the vertical columns are called as groups.
The elements in the same column or group have similar number of valence electrons as thus they have similar chemical reactivity.
