Elements that are most likely to gain two electrons when forming an ionic bond are those in Group 16 (VIA) of the periodic table, also known as the chalcogens.

Here's why:

* Electron Configuration: Chalcogens have six valence electrons (electrons in their outermost shell). They need two more electrons to achieve a stable octet configuration, like the noble gases.

* Electronegativity: Chalcogens have relatively high electronegativity, meaning they have a strong attraction for electrons.

* Ionic Bonding: When they bond with metals, they readily gain two electrons, forming an anion with a -2 charge. This creates a stable ionic bond.

Examples of chalcogens that gain two electrons:

* Oxygen (O): Forms oxide ions (O²⁻)

* Sulfur (S): Forms sulfide ions (S²⁻)

* Selenium (Se): Forms selenide ions (Se²⁻)

* Tellurium (Te): Forms telluride ions (Te²⁻)

Let me know if you'd like to explore other examples or learn more about ionic bonding!