1) which action defines a double-displacement reaction?

a) breakdown of only one compound

b) formation of a precipitate

c)release of light

d) use of oxygen as a reactant

formation of a precipitate

Explanation:

When two salt solutions are mixed, an observable reaction is seen when two types of ions attract each other, they clump together and fall to the bottom of the container as a solid precipitate.

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.