The balanced symbol equation for the reaction of calcium (Ca) with oxygen gas (O₂) is:

2Ca(s) + O₂(g) → 2CaO(s)

Here's the breakdown:

* 2Ca(s): Two moles of solid calcium.

* O₂(g): One mole of oxygen gas.

* 2CaO(s): Two moles of solid calcium oxide (lime).

This equation is balanced because there are equal numbers of each type of atom on both sides of the equation.