If atmospheric pressure measurement for taking at regular intervals from sea level to the stratopause The measurements with most likely show that the pressure

Troposphere

Explanation:

The troposphere is the lowest layer of Earth's atmosphere that extends from under the stratosphere down to the surface of the earth. Nearly all weather condition takes place in the troposphere. The troposphere contains about 75% of the atmosphere's mass and 99% of the total mass of water vapour and aerosols in the atmosphere.

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.