The chemical equation you provided represents the combustion of propane (C3H8) with oxygen (O2). To determine the number of elements involved, we need to identify the unique elements present in the equation:

* Carbon (C): Present in C3H8 and CO2

* Hydrogen (H): Present in C3H8 and H2O

* Oxygen (O): Present in O2, CO2, and H2O

Therefore, there are three elements involved in the chemical equation: Carbon, Hydrogen, and Oxygen.