What is ionization energy and how does this term relate to the reducing property of metals and its trend across a period or down a group?

Hint: To answer this question, you must recall the trends in the properties of the elements in the modern periodic table. The periodic table is the arrangement of a total of 118 elements according to their number of protons or electrons present. It can be broadly classified into four different blocks namely the s- block, p- block, d- block, and f- block.

Complete answer:
The modern periodic table is drawn and arranged according to the modern periodic law which proposes that the properties of all elements are the periodic functions of the number of protons present in their nucleus or the atomic numbers of the elements. The majority of the properties and behaviors of an element are decided by the electronic configuration of that element.
Ionization energy can be defined as the energy that is required to remove an electron from the valence shell of an isolated atom in the gaseous state. More is the ionization energy, more difficult it is to lose an electron, and thus more is the electronegativity of the element.
As we move across a period, the electronegativity increases, and thus, the ionization energy also increases. Down the group, a decrease in the electronegativity is observed and thus, the ionization energy also decreases down the group.

Note:
The modern periodic table consists of 118 elements arranged in a total of eighteen groups and seven periods. The vertical columns represent the groups and the horizontal rows represent the periods. We know there are four different blocks in the periodic table. Each block corresponds to the filling of electrons in the corresponding orbital as mentioned in their name.