Final answer:
The commonly shared oxidation state for Pb, Zn, and Co is +2, as it is observed in known compounds such as ZnCO3 and CoBr2, where these elements have an oxidation state of +2.
Step-by-step explanation:
The oxidation state that is commonly shared by Pb, Zn, and Co is +2. This is because Zinc (Zn) always has an oxidation state of +2, as shown in compounds like ZnCO3 where zinc balances the -2 charge of the CO3 anion. Similarly, cobalt (Co) is known to have the oxidation states of +2 and +3, as in CoBr2 where cobalt has an oxidation state of +2 to neutralize the -2 charge from two bromine anions. Although Lead (Pb) can have both +2 and +4 oxidation states, +2 is the shared oxidation state among these three elements. Therefore, option A, +2, is the correct answer.