Hree friends are talking about what they think causes shiny pennies to turn dull. Deandre says, "I think they turn dull because they're exposed to the air over time." Jamie says, "I think they turn dull because they get dirt on them from being dropped on the ground." Selina says, "I think there is dull metal inside the penny the entire time." Who do you agree with most and why?

Deandre is correct.

Explanation:

When shiny pennies turn dull, due to getting rust. It gets cover with a layer of black or brown color on its surface on the exposure of air.

In this problem,

Deandre says, "I think they turn dull because they're exposed to the air over time." Jamie says, "I think they turn dull because they get dirt on them from being dropped on the ground." Selina says, "I think there is dull metal inside the penny the entire time.

Out of three friends, Deandre is correct. Shiny pennies turn dull because they're exposed to the air over time.

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.

answer:

technetium is the most reactive. this is followed by silver. the least reactive out of these three elements is strontium.