Simplify the following text for a Grade 7 native English-speaking person.
Original: Other oxides are occasionally used , such as MnO2 in manganese thermite , Cr2O3 in chromium thermite , or copper ( II ) oxide in copper thermite , but only for highly specialised purposes . All examples use aluminium as the reactive metal .
Simplified: The metal has to be more reactive than the metal in the oxide , or the thermite will not work .