Which substance can be decomposed by chemical change? 1)ammonia
2)aluminum
3)magnesium
4)maganese

1) ammonia

Explanation:

Decomposition is usually only possible for compounds and of all the options, AMMONIA (Option 1) is the only compound (the other options are elements).

The decomposition of ammonia is a mildly endothermic process, yielding hydrogen and nitrogen gas:

             2NH₃ → N₂ + 3H₂  

It is a mixture. simply put, a compound must be pure, that is, of only one chemical structure and composition. a mixture is made of different chemical substances (i.e. elements, molecules, compounds) that are not chemically bonded to each other, but instead physically grouped together, as in the case of gasoline (a homogeneous solution).