Is rust formation an endothermic reaction because it absorbs energy?
Rust is exothermic.
Rust is the chemical reaction between Iron and Oxygen.
Do a simple experiment. Put some steel wool ( finely spun Iron) in a very hot flame. ( bunsen burner, propane torch.)
The steel wool will start to burn it will glow red even when removed from the flame. The steel wool will turn grey
This experiment will demonstrate that the reaction between Iron and Oxygen is exothermic.