How to remember how a metal reacts with oxygen (or air)

| Metal | + | Oxygen | → | ..? ..It has to be metal oxide! |
(What else could it possibly be?)
Example:
| Potassium | + | Oxygen | → | Potassium oxide |
| 4K | + | O2 | → | 2K2O |

| Metal | + | Oxygen | → | ..? ..It has to be metal oxide! |
(What else could it possibly be?)
Example:
| Potassium | + | Oxygen | → | Potassium oxide |
| 4K | + | O2 | → | 2K2O |