How or why does lead affect blood flow?

lead causes vessels to constrict, limiting the space for blood to flow (compare the size of the red circles.) This narrowing increases blood pressure, forcing the heart to work harder.

By mimicking calcium and increasing cell stress, lead causes vessels to constrict, limiting the space for blood to flow. This forces the heart to work harder because the narrowing increases blood pressure.

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.