A runner completes a 400-meter race in 2.5 mins. What is the runner's average speed?

altitude, density, pressure

air gets less dense the higher the altitude and also the air pressure is less as altitude rises.

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.