Which substance cannot be broken down by chemical changes? Magnesium Hydroxide Carbon Dioxide b O Ammonia Iron

Iron

Explanation:

The only substance that cannot be broken down by a chemical change is Iron.

Iron is an element and elements are made up of atoms. Atoms are the smallest indivisible particles that takes part in chemical reactions.

2h2o2--> 2h2o + o2

this reaction is of the spontaneous decomposition of hydrogen peroxide down into water and oxygen.

add 2 molecules of hydrogen peroxide and 2 molecules of water. since oxygen is naturally diatomic, the total number of atoms of each element is now the same on both sides of the equation so it is balanced.

this may not be entirely correct but let me know.