Heating table sugar.
Dissolving salt in water.
Crushing a can.
Gas burning on a stove
Rust forming on an iron fence
Salt dissolving in a glass of water
Using electricity to break down water into hydrogen and oxygen
Oxygen and copper are examples of elements.
Elements are pure substances.
Atoms of different elements can combine to form compounds.
Atoms of different elements are the same.
State of matter.
Here's an interesting quiz for you.