You add 5.5 gg iron to 28.00 mLmL of water and observe that the volume of iron and water together is 28.70 mLmL . Calculate the density of iron. Express your answer to two significant figures with the appropriate units.

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.