When blood passes through the lungs, carbon dioxide and water are formed from carbonic acid dissolved in the blood. the carbon dioxide formed passes into the lungs and is exhaled.
h2co3 h2o + co2
what kind of reaction has occurred?

decomposition

Explanation:

Decomposition is a type of chemical reaction in which one reactant gives two or more than two products.

The given example is decomposition of carbonic acid to produce water and carbon dioxide.

is an example of decomposition as one reactant is converting into two products by absorption of energy.

your picture is not part of the scientific method.

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.