It's not accurate to talk about the "most common" oxidation valence number in the periodic table. The oxidation state of an element is highly variable and depends on the specific chemical environment it finds itself in. Here's why:

* Electronegativity and Bonding: Oxidation states are assigned based on the relative electronegativities of the atoms involved in a chemical bond. The more electronegative atom in a bond is assigned a more negative oxidation state.

* Variety of Compounds: Elements can form a wide range of compounds, leading to diverse oxidation states. For example, iron can exist in +2, +3, and even higher oxidation states depending on the compound.

* Group Trends: While there are general trends in oxidation states within groups of the periodic table, these are not absolute rules. For example, alkali metals (Group 1) generally have +1 oxidation states, but some can exhibit unusual oxidation states in specific compounds.

* Transition Metals: Transition metals are particularly notorious for having multiple possible oxidation states. This is due to the availability of d-electrons for bonding.

Instead of "most common," it's more helpful to consider common oxidation states for specific groups or elements. Here are some examples:

* Group 1 (Alkali Metals): +1

* Group 2 (Alkaline Earth Metals): +2

* Group 17 (Halogens): -1 (except in compounds with oxygen where they can have positive oxidation states)

* Oxygen: -2 (except in peroxides where it's -1)

* Hydrogen: +1 (except in metal hydrides where it's -1)

Remember, the oxidation state of an element is a useful concept for understanding chemical reactions, but it's not a fixed property of the element itself.