Hi guys. First Post.
I also had trouble with this question.
At first sight I thought combustion obviously because of the heat. But because the product didnt contain water it isn't combustion.
I believe decomposition could be answer but that would only be throught heat. Just having decomposition as an answer isn't correct because it just states the breaking down but not the actual process. Thermal decomposition is correct but decomposition isn't.
We asked our science teacher yesterday and we gave her the equation and she said impossible: decomposition. Combustion she said would only occur if product was metal-oxide + water which it wasn't. Therefore she said answer is corrosion.
To make sure I will ask my head teacher for science. See what she thinks.
BTW i put corrosion
LOL nearly changed to Carbonate reaction