Helium and carbon dioxide
Hydrogen and Oxygen
Hydrogen and carbon dioxide
It smells bad.
Hydrogen is a purple gas and can stain objects that it comes in contact with.
It is too light, one small balloon filled with helium is enough to lift a car off the ground
It is flammable
Salt
Baking powder
Washing powder
Toothpaste
Yeast
Elements
Water
Atoms
Cells
Mercury
Zinc
Lead
Magnesium
Ice melting
Baking soda reacting with vinegar
An egg being fried
Magnesium ribbon being burnt
The substance must be an element.
The ingredients can be separated.
The substance cannot be split up easily.
The substance must be a compound.