The correct formula for the compound formed when lithium (Li) and oxygen (O) combine is Li₂O. Here's why:

* Lithium (Li) is a metal in group 1 of the periodic table, meaning it has a +1 charge when it forms an ion (Li⁺).

* Oxygen (O) is a nonmetal in group 16, meaning it has a -2 charge when it forms an ion (O²⁻).

To form a neutral compound, we need two lithium ions (2 x +1 = +2) to balance the charge of one oxygen ion (-2). This results in the formula Li₂O.